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Articles in this Issue:

We've been busy making all kinds of improvements for our customers, it's hard to know where to begin. I guess the best thing about our web site now is we have taken the Volvo Penta flipcharts (reference pages for each engine) and turned them into a quick-to-use database. Of course we strive to be #1, and as I boast to folks on the phone "Volvo Penta just loves us." It's true: there is no substitute for a well-thought-out reference solution when it comes to ordering parts. We give you two ways now to find the parts you need. The Repair Wizard is still right where it always was, and now the One List seems to have made life easier for a large group of our customers. So, as I keep saying on the phone: "you're welcome" You'll get more of the same in the near future for Pleasurecraft, OMC and other parts as we get the data into the database.

I hope you have a wonderful winter, (or in Australia, a wonderful SUMMER--yes we are quite envious) and that when you have marine engine, transmission, sterndrive or prop needs you will check our web site or give us a call (877-621-2628) This is our "off season" and we have time to chat and would welcome a call from any of our friends, both old and new.

Enjoy the articles and keep coming back!
J. D. Neeson
President, Marine Parts Express


By Robert Van Brunt
Chief Petty Officer U.S.G.G. ret

A Marine Surveyor is retained by a client (boat owner or boat buyer) to verify the value, condition, construction and safety of a vessel as per the American Boat & Yacht Council standards & U.S. Code of Federal Regulations.

At the present time, four organizations certify Marine Surveyors, S.A.M.S., N.A.M.S., A.C.M.S and U.S.S.A. Each have there own standards and are recognized by most lenders and insurance companies (no federal license is required).

Now at this time we'll talk about surveying a 18' to 26' boat with a
gas powered engine and a sterndrive (Diesel engines, because of their
complex fuel injection system and higher compression ratios need a factory trained technician to ascertain the condition of the engine).

A) First the Surveyor will visually inspect the following using the following cited Federal Regulations (CFR) and recommendations of the American Boat and Yacht Council (ABYC):

1. Flame Arrestor (click on my article in The Express, Vol. 1, No. 2) 46 CFR 162.042
2. Bonding & Grounding, ABYC Ch. E2
3. DC Wiring System, ABYC Ch. E9
4. Ventilation, ABYC Ch. H2
5. Cockpit & Scuppers ABYC Ch. H4
6. Gasoline Fuel Sys. ABYC Ch. H2
7. Thru Hull Connections ABYC Ch. H24
8. Storage Batteries ABYC Ch. E10
9. Hull Idenification Number 33 CFR 181
10. Safety Equipment 33 CFR & 46 CFR

While many of the above may seem to be common sense there are specific details that may make your boat not only unsafe, but also un-insurable.

B) Next the Surveyor will inspect the boat’s Hull - checking for water intrusion in the foam core and transom laminates. Some manufactures build a monolithic cored transom, then make a large cut out for the stern drive often leaving unsealed plywood surfaces (see my photo).

(click to enlarge)

Improper installation of any screws or bolts can also allow water to enter the hull coring. To determine if this has happened the Surveyor has two techniques to find moisture in the laminates. The old method is tapping with a hammer and listening to the hull sound. The new Higher Tech way is to use a Capacitance Moisture Meter (not a wood type Resistance Moisture Meter). This testing can tell you if you are likely to need high price fiber glass repairs in the future.

C) The Stern Drive is now the subject of out of the water inspection. The Surveyor will look at the lower gear case very carefully. Bondo and spray paint can skillfully cover up impact damage (hit a rock!). Pressure testing and vacuum testing the lower gear unit will indicate the integrity of the shaft seals. The prop shaft should be tested with a Dial Indicator; most manufactures allow only a .003" to .005" shaft run out.

D) The Surveyor will now get real serious and check out the boats performance with a Sea Trial. The vessel should achieve the engine manufactures rated RPM, without over-heating for at least a half hour run! The installed dial tachometer will be compared to a calibrated digital Photo Tach or digital Inductive Tach (installed dial tachs are notoriously inaccurate). Temperatures can be compared to a laser infrared Thermometer or a calibrated HG lab Thermometer. Boat speed can be established by hand held GPS or by the old fashioned, but accurate stop watch method.

If the engine will not achieve rated RPM or operating temp is incorrect the Surveyor will check the following and compare with manufactures’ recommendations:

1) Designed Trim
2) Propeller Over Pitched (See Propeller Sizing in the issue)
3) Ignition Timing, Check with Timing Light (check that spark plug wires are installed in the proper order}
4) Vacuum, on carbureted engine test with Vacuum Gauge
5) Compression, Test with Compression Tester
6) Spark Plugs, Inspect and compare
7) Check Sea Strainer for debris & air tightness
8) Check Thermostat for proper operation
9) Check Sea Water Pump for proper operation. (See Pump Article)
10) Heat Exchanger, core may have to be removed & cleaned

A Surveyor will usually charge by the foot (between $30 - $50 a foot), but it is money well spent compared to the price of replacing a drive or an engine.

1. NAVTECH Marine Surveyors Course
2. USCG Boating Safety Manual M16750.4
3. ABYC Small Craft Standards
4. Chilton’s Auto Repair Manual (Gas Engine Testing)
5. Professional Boat Builder Mag (Drive Unit & Hull Testing)


By J. D. Neeson
President, Marine Parts Express

Every engine has a maximum horsepower rating and a maximum Revolutions
Per Minute (RPMs) that permits the engine to meet that horsepower rating. It is important that the outdrive ratio (or transmission ratio for inboards) and the propeller size allows the engine to reach this maximum.

So when a boat is going at full speed (the term often used is Wide Open Throttle or WOT) the RPMs shown on the tachometer should be the same as the maximum RPMs provided by the engine manufacturer.

1) If, when at WOT, the RPMs on the tach (always calibrate your tach to be sure it is correct) are higher than the manufacturer's maximum RPMs, it means that either the outdrive ratio is too high or (more likely) the prop is too small. Most often the prop is incorrect. Manufacturers are very careful about matching engines with the proper drive (or transmission) ratios.

Using an undersized prop is bad for your engine. The engine will over-rev and operate over the design specification for the engine. A comparable metaphor would be driving a car at 60 miles an hour in second gear.

2) If, when at wide-open throttle, the RPMs on the tach are less than the manufacturer's maximum RPMs, it means that either the outdrive ratio is too low or more likely, the prop is too large. Again it is almost always the prop size or pitch (or both) that is incorrect. It is like trying to drive a car up a steep hill in fifth gear.

Using an oversized prop is also bad for the engine because overloading the engine will eventually cause damage to the bearings and cylinder walls. In addition, when a prop is oversized, the boat will not go as fast as it is designed to go as the engine is not strong enough to turn the oversize prop.

The relationship between prop size and RPMs is clearly seen at WOT but it exists at all RPMs (speed). If the prop is too big, the engine has to work harder than it otherwise would to get to a certain speed. If the prop is too small then the engine has to run faster than it really should to attain a certain speed.

A rule of thumb for single props is: for every 1" change in your prop size the RPMs change between 400-500 RPMS. Every 1" in pitch your RPMs will change between 150-200 RPMs.

With dual props however pitch changes are measured as a function of both props. Therefore, the change is approximately 70% that of single props. So the change is 280-350 RPMs and 105-140 RPMs respectively.

However, these numbers are just approximations and should be used as benchmark guidelines and not specific recommendations. The length, weight and type of hull of the boat can change these ranges as well as the horsepower and ratio of
your outdrive and transmission.

Get the most out of your boat!
Please contact us and give us specific information about your boat if you have questions about propping. We would be happy to share our experience in this area with you and help you get the propeller you need..


By Robert Van Brunt
Chief Petty Officer U.S.G.G. ret

The Electronic Control Unit (ECU) or Electronic Control Module (ECM) (In this article we are using Volvo terminology, but all manufacturers now have similar control.) controls the fuel air mixture and spark advance or retard. It also stores data from the engine sensors. This data can be retrieved from the ECM using the DLC connector (the automobile DLC has 12 pins; the marine DLC has 10 pins). The technician attaches a scan or code tool to the DLC and can determine the operation of all the controlling sensors.

The automotive ECU has an exhaust oxygen sensor which maintains a fuel air mixture of 14.7:1 at full load, so that the catalytic converter will operate at full efficiency. Automobiles also have an AC on/off sensor and a MPH sensor. None of these however are used on the Volvo Penta Marine Engine system.

The Volvo Penta ECM has the following sensors to control engine operation.

MAP: Manifold Absolute Air Pressure, measures engine load and controls fuel mixture & spark advance.

ETC: Engine Coolant Temp, measures engine coolant temperature and controls fuel mixture, spark advance and idle speed.

TP: Throttle Position Sensor, measures throttle position to control acceleration & idle speed.

KS: Knock Sensor, detects detonation in the combustion. This input will make the ECM enrich the fuel air mixture by 7% and retard spark timing to the maxim of 10% to stop the detonation.

RPM: Engine Revolutions per Minute: input from the Ignition Control Module.

New at the Marine Parts Express Site:
Onboard Kits updated
One List updated

Coming soon:
Manifolds page, PCM List, Mercury props page

Express author Robert Van Brunt (Chief Petty Officer, U.S.C.G. ret) is a member of the American Boat and Yacht Council and a member of the International Association of Marine Investigators.

Comments? Questions? Suggestions for topics in our next newsletter? Send them to Marine Parts Express is a division of Water Resouces, Inc., a privately held Maine Corporation.