Surveying the Stern Drive Boat
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).
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)
Comments? Questions? Suggestions for topics for our blog or newsletter? Send them to
Marine Parts Express is a division of Water Resources, Inc., a privately held Maine Corporation.
For all your marine engine parts needs, call us toll free at 877.621.2628, or outside the U.S. at 207.882.6165.
August 7, 2010 / mpartsexpress / 0
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