Engine in a Box

Notes and observations

Online you can find just about anything you want concerning the engine in your boat. Just type into the search engine the make and model and you can find an enormous amount of information. This page concerns itself with the cage (engine room) that this animal (gas or diesel) has to live in. Plus, how to give it the best care and feeding possible, before you have to climb in there and play doctor to it.

First, like any breathing thing, it’s got to have air. The power rating of marine engines, which is regulated by the volume setting of the fuel injection pump, is set for the climatic conditions in which they are to operate. Usually, factory settings are at 60F to 70F. If the air in the engine room becomes unduly heated, the engine is unable to induct sufficient weight of air to provide complete combustion of its designed fuel injection volume and it will not develop its designed horsepower and R.P.M. The “British Standard” of derating for atmospheric temperature is 2% per 10°F and it will readily be seen that if an engine be operated in a 120°F atmosphere when it is designed for a 60°F atmosphere it should have its fuel supply reduced by 12% and, consequently, its power output reduced.

The atmospheric pressure, temperature and humidity all affect the density of the air. On a hot or a moist day, the air is less dense. That reduction in air density reduces the amount of oxygen available for combustion and therefore results in incomplete combustion and reduces the engine horsepower and torque. For tweaking the fuel/air mixture, the air density is the most important consideration.

This incomplete combustion has a cumulative effect on engine room temperature. The products of incomplete combustion can cause lubricant contamination, internal deposits and fouling, also high piston, valve and sprayer temperatures, etc., and may lead to unreliability and high maintenance.

So, when your down in the engine room or open that little engine hatch, how hot is it in there? Most of the ones I’ve been in, seem like a Turkish bath. What can you do? First, check to see where the engine air intake gets its air from. If it’s the cage (room) itself, how about making sure that it has some nice intake and exhaust air supply hoses. Preferably, that intake hose is real close the air filter/intake on the engine. That air is maybe 30-40 degrees cooler than the rest of engine room. If it’s a long intake hose, make sure it’s has straight as possible to that nice big dorade on deck.

No so good to have a 6” hose for a 300 horse power engine that runs 8 feet with three, 90 degree turns and hooked to a low profile dorade that has a cooler in front of it! Kinda like you or me breathing out of a 8 foot straw! Do you have too many bends, small diameter hose; think about adding a power fan to it. I installed one to a 6" hose on a 50 horse power engine (an engine compartment vent fan, mounted in reverse) cruising the South Pacific and it helped with engine combustion and cooling the boat at its heat generating source, the engine. Basically, you want to get that air filter to get the most and the coldest air possible. (That’s part of what a turbocharger and intercooler is about) Of course, you must ensure the air filter is cleaned regularly.

So now that it’s breathing OK, what are we feeding it?

Some diesel engine problems are related to fuel problems and now "oxygenated" gasoline is having some of the same issues.  Diesel fuel contamination problems have two different perspectives: biology and chemistry. Thinking you have a chemical problem when you have a biological problem and treating it with the wrong chemical cleaner will not solve your problem and may compound it.

The most prominent problem is chemical and lies in the creation of "asphaltene." Asphaltenes (aka diesel sludge) looks like algae but there is NO ALGAE in diesel fuel. Asphaltenes are created by either the natural aging of diesel fuel, by simply adding the wrong fuel additives or mixing perfectly good clean fuels from two different suppliers. As the fuel further deteriorates, it darkens, produces a foul odor, and often causes diesel engines to smoke. This is a direct result of the early-stage fuel clustering and passing through the filtration systems and into the combustion chamber. These clusters cause greater difficulty as they increase in size, failing to burn correctly, thereby exiting the system as unburned fuel in the form of smoke. This problem is exacerbated as the clusters eventually reduce the fuel flow to the point of clogging the filters. Filtration does not solve the core issue of excessive sludge in the fuel and tank.

The other problem that affects diesel fuel is a biological problem... "Fuel Bugs." There are many types of Fuel Bugs (aka bacteria, fungus and mold), that can live in diesel fuel. A small amount of water from either condensation or from entering the tank through a vent can start your Fuel Bug colony growing. "Fuel Bugs", bacteria and fungus, primarily Cyanobacteria, in diesel fuel are less prominent that Asphaltenes. Most diesel users have very little knowledge of this costly problem. There are over 100 types of Fuel Bugs that can live in diesel fuel. Fuel Bugs feed on the oil in the fuel and use the water in the fuel for their oxygen supply. They grow in your fuel at different rates and can easily cost thousands of dollars in damage.

So, fuel filters are a start. High quality remote Racors or even those inexpensive ones you can by at NAPA will help keep the engine running, till they clog! You can use asphaltene dispersants and fuel biocides, but make sure you know what the problem is!  If the fuel tank is badly contaminated you could install one of the new onboard fuel treatment systems or you can try fuel polishing. Then, you must treat the fuel continually. Biocides eat bugs and when those few ounces of biocides you added to your fuel tank have eaten all they can, they full and you have to add more biocides. Also, when you add the sludge dispersant to your 500 gallon tank, then used 150 gallons, and then let it sit again, it just got older and dropped out more asphaltenes. The fuel is never in a stagnant state, it may be changing slowly, but it’s changing.

ALERT! ETHANOL IN HAWAII

For those having gasoline engines, inboard or outboard, I have added some info from the petroleum, ethanol, engine, and marine industry. Read this stuff and check the internet for your particular engine, boat fuel tank, etc.

Beginning April 2, 2006, at least 85 percent of Hawaii’s gasoline must be E-10 Unleaded: gasoline containing 10% ethanol. Ethanol, a renewable fuel, is a normal component of today’s gasoline. All gasoline-powered vehicles sold in the United States are designed to use E-10 Unleaded. Gasoline containing up to 10% ethanol has been in increasing use in the United States since the late 1970s. In 2005, about 40% of the gasoline used in the U.S. contained ethanol.

In some states and large metropolitan areas, all of the gasoline contains ethanol, and has for several years. Blends have been available in over 41 states for more than 10 years, and in over 21 states for more than 20 years. Information from these areas can help Hawaii gasoline retailers, automotive industry, regulators, and the public to become familiar with the fuel.

What is ethanol, and ethanol-blended fuel?

Ethanol is highly refined beverage (grain) alcohol, approximately 200 proof, and can be made from natural products such as corn, sugar, and wheat. Ethanol that is used for fuel has been denatured with hydrocarbon, rendering it unsafe to drink.

E10 Unleaded fuel is a mixture of 10% ethanol and 90% unleaded gasoline (E for ethanol and 10 is for 10%). Automobiles that normally use unleaded gasoline for fuel can also run using E10 fuel. E10 is NOT considered an alternative fuel (it's still 90% gasoline).

Another type of ethanol-blended fuel is E85. E85 refers to a mixture of 85% ethanol and 15% unleaded gasoline. E85 is an ALTERNATIVE FUEL and is for use in ALTERNATIVE FUEL and FLEXIBLE FUEL vehicles.

FUEL FILTERS
Several issues come into play with fuel filters and the conversion to an ethanol blended fuel. There is a sediment issue when an ethanol conversion first takes place. Ethanol acts as a cleaning agent, breaking loose built-up sediments from the tank and other areas and leading to an initial period where fuel filters tend to clog (the same can also happen in automobiles). After the sediment has worked its way out, Does ethanol lead to plugged fuel filters?

Ethanol is an efficient solvent, and therefore, the use of ethanol-blended fuel may result in loosened contaminants and residues collecting in the fuel filter. The fuel filter may need to be changed following the first full tank of ethanol-blended fuel has been used. After this, the fuel filter's normal maintenance schedule may be followed. This problem is very uncommon, and is likely to happen only in older cars that used leaded gasoline water becomes a consideration.

FUEL TANKS

BoatU.S. Magazine has recently reported a preliminary investigation into claims about gasoline containing ethanol causing older fiberglass fuel tanks to fail. The ethanol additives could reportedly lead to weakened tank walls and bottoms that potentially could lead to a leak or explosion.

Industry-wide changes in fiberglass resin formulations made in the mid-1980s could be a beneficial ally in correcting this condition. The problem appears only to occur in fiberglass tanks manufactured prior to the changes. It is also important to note that diesel fuel systems do not appear to be affected.

In preliminary reports, BoatU.S. did confirmed the claims of gasoline leaking into the bilge following tank wall failure. The reports also indicated a tar-like substance that produced hard black deposits which destroyed the engine through continual damage to the intake valves and pushrods. BoatU.S. speculates the tar-like substance is created by a chemical reaction between the older fiberglass resin and the ethanol.

Boat owners should be aware of signs of engine backfiring and hard or sluggish starting in which the motor turns over slowly as though the battery is weak. In addition, affected engines may not reach their rated RPM. Chuck Fort, associate editor of Seaworthy, the damage avoidance newsletter from BoatU.S., stated, “Ironically, the substance seems to pass through fuel filters leaving no tell-tale marks – some have appeared clean on our reports. The only way to know for certain is to pull the carburetor and inspect the underside for a black, gummy film which can indicate a serious problem.” BoatU.S. is recommending all early 1980s or early vessels with fiberglass gas tanks be stored empty over the winter.

The investigation is ongoing, but it appears that 10% ethanol gasoline, which was introduced in the Long Island area to replace gas additive MTBE in late 2004, may be attacking the resins used in older fiberglass gas tanks. These tanks were standard equipment on some Hatteras and Bertram models and may be present on other boats of the same era. Diesel tanks are not affected.

The engine damage appears to be due to a tar-like substance--possibly from the chemical reaction between the resin and ethanol--causing hard black deposits that damage intake valves and pushrods, ultimately destroying the engine. Early symptoms may include engine backfiring and hard or sluggish starting in which the engine turns over slowly. Affected engines may not reach their rated rpm.

Technical info:

The Aussie government on outboards,

http://www.deh.gov.au/atmosphere/fuelquality/publications/assessment-e10-e20/mercury.html

and the engineering department of Dartmouth College. (This is a 117 page download)

 http://www.google.com/search?hl=en&lr=&ie=UTF-8&q=related:www.dartmouth.edu/~ethanolboat/Ethanol_Outboard_Final_Report.pd

What is phase separation?

When E10 fuel is contaminated with over 0.5% water, the ethanol and water mixture will separate from the gasoline and fall to the bottom of the gas tank. The fuel system must then be drained and new fuel added. Before using ethanol-blended fuel for the first time in an older small engine, all water should be removed from the tank.

What do we do now?

For now, as of the end of March 2006, not a lot can be done for that fiberglass tank. The application of some type of coating to the interior of a FRP tank would be the easiest even with the additional labor of cutting off the top for access. The problem is, no coating is available as yet, WEST SYSTEMS says no...

All types and variations of tanks have been successfully constructed with WEST SYSTEM Brand epoxy and used in the field with great results. However, Gougeon Brothers does not condone or recommend that certain tanks be built because of various issues noted above. In our testing, various epoxy combinations have proven to be resistant to various liquids, including gasoline, diesel fuel, motor oil, potable water, sea water, sewage, gray water, etc. Regarding gasoline specifically, some epoxy combinations are more resistant than others. With the increasing use of alcohol and other high-tech additives, we are unsure how the epoxy will resist them in the future. We do know that many types of alcohol vigorously attack epoxy; we can only conclude that gasoline with a higher percentage of alcohol may break down an epoxy coating over a long period of time.

So for now, Watch your fuel filters!

                  Watch for fuel leaks!

                  Watch for performance issues!  

If you have older fiberglass built-in fuel tanks, maybe you need to think about that time when you will have to replace with a metal tank. As soon as I hear something that is proven to work, I will post it on the site.

OK, we got that caged animal breathing correctly; we got it some good food, next, how about we check the plumbing and make sure we don’t have to clean that cage!

Raw seawater systems are relatively simple. That raw water pump should not leak anywhere, period. Any buildup of salt crystals anywhere, is a leak. The impeller that draws the seawater in must have all its vanes on it or it will cause the engine to overheat. I prefer the “blue” Globe brand impellers; they say you can run them dry for 15 minutes before they destroy themselves, used them cruising the Pacific and every time I popped the cover off, it looked new!  We have to play plumber here and take off the cover plate to check, especially if the engine has not been started in months. Impeller vanes can take a “set” (bend) in the pump. Don’t worry, that plate and the thin gasket, is relatively easy to reinstall.  Also, make sure the zincs in the heat exchanger/transmission cooler are still there. Don’t want to buy a expensive heat exchanger because of a couple of $3 zincs! Check the exhaust mixer, hoses and clamps for leaks and part one is done.

Part two is the fresh water side of the exhaust.  A 50/50 mix of antifreeze and water is best, according to most engine manufacturers. Straight water provides no freezing, boil over or corrosion protection. It also cools less efficiently than the 50/50 mix. It is best to use distilled water because it is pH neutral, contains no acids, dissolved salts or minerals and maximizes the coolant life. If you are using a “long-life” antifreeze, do not mix it with regular antifreeze and visa versa. They are both made with different ingredients that may neutralize the corrosion inhibitors and would contaminate the system. If that happens you will have to drain the complete system and start again.

Long-life antifreezes advertise they are good for 3-5 years; regular antifreezes are usually only good for 1 year, whether the engine is run or not! The corrosion inhibitors dissipate so just because it looks green or red or yellow, does not mean its protecting the engine from corrosion. You will have to add more corrosion inhibitors or drain and renew the system.

To add more inhibitors and combat corrosion, one must monitor the rate of corrosion within the cooling system. The rate is caused by a number of factors, including the acidity or alkalinity of the coolant. The acidity and alkalinity is measured on a pH scale and is very important. If the coolant remains alkaline, corrosion is inhibited but if it becomes acidic, the coolant begins to eat away at the interior of the system. Test strips are available online or at some auto parts stores and it’s a simple test. Also, if your engine does not have an overflow system, add one! The local auto parts store sells a complete kit, plastic tank, bracket, and hose for under $20 and it's a whole lot easier and safer to glance at the overflow tank to see if the coolants low, dirty, etc.

The last check is that expansion tank/radiator cap, the cheapest moving part of the system. When I do an engine analysis I pressure check the system and many times that 7 lbs. or 13 lbs. cap will not hold is rated capacity (Gee, it's 10-15-20-30 years old). Freshwater system are designed to hold a certain amount of pressure caused by that water/mixture and heat, add a faulty cap, engines overheat, loose coolant, etc.etc. Stamped right on that cap is the pressure capacity, the auto parts stores even have them new fangled caps with the pressure release levers for about $7.00, can make a world of difference!

Wet Exhaust Systems

Carbon monoxide poisoning, excessive heat in compartments, and reduced engine performance can develop from the lack of good exhaust system maintenance. We’re not talking about anything more extensive then taking a look once in awhile. Which is usually the problem! A good surveyor will climb around down there and look, grab, and/or shake every hose clamp and fitting when the engine is cold and look at them again when the engine is running. It would be nice to think I never come across problems in exhaust systems but that’s not the real world. Sometime everything appears fit for service until I run a CO meter at those same fittings and it detects leaks. Most of the time, just enough to give you a really crappy headache at the end of your day on the water. So, what to look for…

Exhaust Manifold - Check the tightness of the attachment nuts and bolts especially on engines which have heavy manifolds that incorporate header tanks and heat exchangers. Leaking manifold gaskets are the first signs of loosening.

Freeze Plugs - Check for salt and corrosion on them little round disks. First signs are usually pin-prick sized holes, or bubbling of surface paint.

Exhaust Injection Elbow - Salt or corrosion indicates a leak caused by severe corrosion. First indications are usually small pin-prick sized holes adjacent to the point where raw water is injected into the elbow. Soot deposits by the mounting flange indicate a loose joint or gasket failure. Check tightness of attachment bolts which loosen through high temperature and settling of thick gaskets. Lots of engine manufactures suggest you remove and inspect internally every other season.

Hose Clamps - Inspect for corrosion and cracking. Those nice shiny clamps with the rusted (not stainless) screws… usually snap or strip when you want to tighten them up some.  NFPA 302 4-3 says exhaust hose should always be double clamped at every fitting throughout it’s’ length. Put those two tightening screws on alternating sides, gives you a little more safety factor.

Lift Box/Muffler - Stainless mufflers suffer from corrosion with stainless corroding from the inside out. I had a boat where the stainless water lift was a foot above the engine, “rusty” on the outside, which really had rusted thru the internal pipe. I turned the engine off and it dropped all its saltwater down the hose, up the injection fitting at the exhaust manifold, thru the manifold and into the cylinders. Seven days, 2 gallons of WD-40, 15 gallons of oil, 4 oil filters, a million pesos ($650 US) and countless rags and cleaning stuff fixed it. Hey, it looked okay to me a 1000 miles earlier when I last checked it. Best fish tacos are in La Paz, while you wait for parts. Plastic lift boxes and mufflers suffer from split welds mostly through over tightening of exhaust hose clamps. Glass fiber boxes are usually maintenance free and provide longer service (part of that $650).

Exhaust Hose - Check for cracking, softness, delaminating, kinking and corrosion of the reinforcing wire. An SAE J2006 spec’ed wet exhaust hose just can’t be strangled, it’s like squeezing a metal pipe.

More info on how to flood your engine-
The raw water flows with the exhaust gases into a water-lift box, also called a water silencer. The discharge pipe of the water-lift box is set slightly above the bottom of the box. The water level rises until it blocks the discharge pipe, at which point the trapped exhaust gases build up sufficient pressure to lift the water up the exhaust pipe and out of the boat. If the engine is installed below the waterline, problems can occur. If the engine is at any time below the waterline, any cooling circuit that allows raw water into the exhaust has the potential to set up a siphon action. Water may siphon in from the water injection side; or, if the exhaust outlet is below the waterline, from the exhaust outlet side. It may be driven up the exhaust pipe by following seas; or, in an otherwise calm anchorage, be forced up the pipe by repeated wakes from passing boats or common wave action. This phenomenon is known as a water hammer. Similarly, on a boat with a generator, backing down can force water into the generator exhaust.

Repeated cranking of a difficult to-start engine can pump excessive water into an exhaust. With every cranking attempt, the raw-water pump will move more water into the exhaust. In a typical installation, this water will not be pumped out until the engine fires by which time; there may be enough water in the exhaust to flood the engine.

A siphon break is a good idea on sail boats and even on some power boats where the raw-water injection point is above the waterline, making the development of a siphon theoretically impossible. I believe the recommended practice is that the injection point is 15” above the waterline. Those "level state;' calculations made by the builder often do not hold at sea. The boat may be heavily laden and down a few inches on its waterline. There may be times when the angle of heel puts the injection point below the waterline, a particularly likely scenario on twin-engine boats, where the engines are offset from the centerline. Or, there may be occasions when substantial waves surging past the boat create sufficient hydrostatic pressure to set up an intermittent siphon, eventually flooding the engine

To finish up… get down there and take a look, or tell that mechanic you dropped a hundred dollar bill and will split it with him if he finds it, or call me.

OIL

With oil at $70.00+ per barrel before refining, it’s not time to be frivolous about crankcase oil. It’s also not time to buy that cheap engine oil you’re going to put into the very expensive machinery and diminish its life span. I came across this website from guy in Europe that explains engine oil, use, history, specification, and done very nicely. http://www.carbibles.com/engineoil_bible.html

My interest with engine oil came from the propane industry 20+ years ago. At the time we were converting gasoline engines to run on gasoline and propane or straight propane. Up to that time as far as I was concerned there were 2 types of oil, oil for gas or diesel engines. Using regular gasoline motor oil in an engine that injects a vapor not a liquid into a cylinder causes big changes. Gasoline and diesel motor oil has an “ash” package additive. Ash is added to oils because of cylinder wash down, (gasoline or diesel that runs down the inside of the cylinder) and drops into the oil pan. No ash in those engines gets you really thin oil, oil so thin it’s not oil anymore, it’s solvent. In our experience with propane, no cylinders washed down because propane is a vapor, the oil is not diluted anymore and now the ash is slowly cooked with engine temperature. You get nice black grease, a “Crisco” kind of thing, also not a engine oil and nearly impossible for an oil pump to push up into the cylinder head!

Why, did I tell you all this? To impress upon you to check your engine manual and if you do not have one, to contact the engine manufacturer, they have specified exactly what oil to pour into that little monster. Have question about using the new synthetics; contact them, especially if it’s still in warranty!

Oil additives are numerous, these are just a few I got from the web and there’s plenty more. Some key types, what they do, what they are composed of, and how they function.

Antiwear and EP Agent - Reduces friction and wear and prevent scoring and seizure. Zinc dithiophosphates, organic phosphates, acid phosphates, organic sulfur and chlorine compounds, sulfurized fats, sulfides and disulfides. Chemical reaction with metal surface to form a film with lower shear strength than the metal, thereby preventing metal-to-metal contact.

Corrosion and Rust Inhibitor - Prevents corrosion and rusting of metal parts in contact with the lubricant. Zinc dithiophosphates, metal phenolates, basic metal sulfonates, fatty acids and amines. Preferential adsorption of polar constituent on metal surface to provide protective film, or neutralize corrosive acids.

Detergent - Keep surfaces free of deposits. Metallo-organic compounds of sodium, calcium and magnesium phenolates, phosphonates and sulfonates. Chemical reaction with sludge and varnish precursors to neutralize them and keep them soluble.

Dispersant - Keep insoluble contaminants dispersed in the lubricant. Alkylsuccinimides, alkylsuccinic esters, and mannich reaction products.

Contaminants are bonded by polar attraction to dispersant molecules, prevented from agglomerating and kept in suspension due to solubility of dispersant.

Friction Modifier - Alter coefficient of friction. Organic fatty acids and amides, lard oil, high molecular weight organic phosphorus and phosphoric acid esters. Preferential adsorption of surface-active materials.

Seal Swell Agent - Swell elastomeric seals. Alkylated naphthalene and phenolic polymers, polymethacrylates, maleate/fumerate copolymer esters. Modify wax crystal formation to reduce interlocking.

Antifoamant - Prevent lubricant from forming a persistent foam. Silicone polymers, organic copolymers. Reduces surface tension to speed collapse of foam.

Metal Deactivator - Reduce catalytic effect of metals on oxidation rate. Organic complexes containing nitrogen or sulfur, amines, sulfides and phosphates. Form inactive film on metal surfaces by complexing with metallic ions.

So, gotta degree in chemistry? I sure don’t. How do I tell if the engine is in trouble from the oil its swimming in? Oil analysis! You bought a nice new boat with an engine, a baseline analysis is a good start, whether the engine was made this year or 20 years ago in a “new to you” boat. With the metal particle information from an oil analysis you can get lots of info on where to go from there and what is happening inside. I used this company, check the info on their website.

http://www.analystsinc.com/  Click on SERVICES, then USED OIL ANALYSIS, then SPECTROCHEMICAL ANALYSIS to see the metal particles they count and where they come from.

Oil Changes

Check your manual (again) they will give you an engine hour time limit. That does not mean “I ran it for 5 hours, 6 months ago, it should be Ok”! That ash additive package I mentioned above may or may not absorb water from condensation. A crankcase is not a completely “seal” system so think of the crank case like a partially covered bucket of oil in your garage. Cruising, (running the engine daily) I changed the oil every 50 hours and never had a problem with that part of the system. I don’t believe you can change it too often in the marine environment, especially small engines. You have 2 huge diesels you say, the big dollar engines? That oil analysis will tell you exactly when! Filters are specified by the engine builder, brands won’t matter much if you change the oil regularly, keep the spares in a zip lock bag so as not to absorb ambient moisture. Cruising, we had them vacuum packed.

Again, monitor that oil, get a baseline oil analysis, then get one in the oil change time limits (specified by the engine builder) to ensure the oil is performing correctly in your particular environment and change the filters often. Otherwise you’re guessing and gambling.  An analysis is much cheaper than a tow or a rebuild.

SOUND

Starting out in power boats then moving to sailboats changed me drastically over the years. I like my vehicle without glass pack mufflers, etc., and don’t want to hear anything but the radio. On boats, any voyage is much nicer when you DON”T HAVE TO YELL to have a conversation. I do decibel tests on every boat survey (see testing methods page) and most levels are at 97dB to 115dB within that engine room, some are lots higher. Cabin spaces are around 80dB and most could be a lot lower. The culprit is usually no or incomplete sound insulation installed by the builder. Completely correctable and easily done with a little time and the correct materials.

Soundproofing involves two concepts that require two different materials with their own rating systems, barriers and absorbers. The NRC number tells you how much sound energy is absorbed (the higher the number, the more absorption), and the STC number rates the amount of sound blocked in decibels (again, the higher the number, the greater the sound absorption). For example, a brick wall has an STC in the 50s, whereas a single-plate glass window's rating may be 30. Another figure to be aware of is the product's flame-retardency rating. Do not install sound proofing materials that are flammable, check that UL fire rating.

What is a NRC number? NRC, or Noise Reduction Coefficient, is the average sound absorption of the four speech interference frequencies (250 Hertz, 500 Hertz, 1000 Hertz, And 2,000 Hertz). A material with an NRC of 0.95 absorbs approximately 95% of the noise that strikes it. That is, it prevents sound from reflecting off it.

The STC number, or Sound Transmission Class, is a single number rating of a material’s ability to stop sound from going through it. It is used to rate doors, windows, walls, ceilings, or any other partition between spaces. Generally speaking, the higher the STC rating the greater the sound reduction. An STC value is a single number rating used to characterize the sound insulating value of a partition (wall, floor, or ceiling). A partition prevents sound from being transmitted from one area to another. The higher the STC rating, the less sound will be transmitted through the wall, floor, the higher the STC value of a floor/ceiling, the better its ability to control impact sound transmission. A rating of 50 or higher is considered acceptable.

56 and up=Excellent    45-55=Very Good    36-45=Good    26-35=Marginal  15-25=Poor    As a reference, you can hear normal speech through a wall with an STC of 25 At an STC of 42, loud speech is audible as only a murmur.

If you were to make a mat of sound absorbing material thicker and use a metal barrier inside it, it would be very effective in really stopping engine noise coming through. So, if ordinary kitchen Reynolds Aluminum Foil is sandwiched between the mats, (use contact cement), most of that noise will be prevented from entering the cabin. A 2" minimum total thickness is recommended. Another is a lead-backed material originally developed for the military. It is expensive and heavy and I have used it in U.S. Navy tour boats with great results.

Suggestion from the guy that has constant ear ringing! Make it easier on yourself and the family, add the sound insulation. HOOK UP or A SANDWICH WOULD BE NICE, sounds more professional WHEN YOU DON’T HAVE TO YELL.

Marine Engine Alarms

I am a big fan of alarms; it's the first thing on a survey that you do not have to inspect with your eyes, magnifying glass, or meter! After looking at the entire engine I can, I turn the key to on. Bells, buzzers, and sirens tell me that if something happens while underway, at least there is some system in place to let me know. Cruising, I even had a 12 volt counter in the bilge pump system to let me know how many times the pump cycled, and it had a piez buzzer with it (which I duct taped over after a knock down in the Coral Sea).

There are a variety of systems available, from the $30 Cole Hersey vibrating relay to the Aqua Alarm 5 sensor system for $300, and I am sure many more. Use one and make it annoyingly loud. It would be nice to hear differences whether it's the water temperature or the engine oil but whatever you can afford. It could be the only thing between you having to buy and install another impeller or rebuilding an engine, or worse. They all seem to tie into the existing oil or water temperature sensors that come with the engine for the gauges so it's not a complicated process.

Years ago lots of power boats had pyrometers in the engines (a thermocouple that installed into the exhaust manifold with a gauge) and some captains swore they could tell you if the prop had picked up a piece of kelp by what the pyrometer temp was. They are still available and if you look at your exhaust manifold you will probably find a square screw in plug where they are installed. Some of the newer monitor systems attach into the exhaust hose and monitor the quantity of water flow out the transom. Never tried one of those, but if you are a gadget person, why not. Some of those freighter and tankers you see on the horizon have a monitor system on each cylinder of their engines that tell them the parameters of every engine stroke. The issue is making sure your alarms function if you have them and install something if you don't.

If you want to see something real different and maybe the future of propulsion systems for recreational boats...

http://www.solomontechnologies.com/m_recreational.htm#multihull

Contact me,

Phone: 808-375-8260 

Email: Bob@BoatSurveysHawaii.com

Robert J. "Bob" Dupuis

Marine Surveyor/Consultant