One point about generating capacity. Some outboards (like the Yamaha) will generate almost the maximum amount at low throttle. Others generate electricty on a more linear basis relative to the RPM (like at least older OMC's). Something you might ask about.
The April 15 issue of Practical Sailor (and a recent prior issue) has a discussion about props on small outboards. For your convenience, I have entered the part from this issue:
PROPER OUTBOARD PROPPING
[Ed}We thought we'd run this valuable letter to follow up our recent discussion of outboard engine power in this column. The issue of prop size and pitch often plays second fiddle to other concerns, but it's central and we thank Mr. Below for covering it for us.
This is in response to Mr. Patrick Green's question about outboard power for a Pearson 26 [PS Advisor, February 15].
[Letter] I owned a 1975 P-26 for nearly 20 years (traded up to a 10-M in '99), cruising Long Island Sound and out to Nantucket. I acquired a '76 9.9-hp Johnson, 20" shaft with electric start, which I used for most of those years. I still own this engine.
The standard propellor for the Johnson was a 91/2" diameter by 10" pitch. This propellor did not allow the engine to reach its intended operating rpm, and as a result the engine fouled spark plugs and would not keep the battery charged. I quickly changed to the optional 10" x 5" "barge" propellor offered by OMC. This low-pitch propellor made all the difference. Plug fouling stopped, and the higher operating rpm allowed the alternator to keep the battery fully charged.
In 1995, I succumbed to the desire to own a more environmentally friendly four-stroke and purchased n 8-hp Honda manual start, 20" shaft. The stock Honda prop was 9" x 10", I believe, and did not allow the engine to reach its recommended operating rpm.
I switched to a 8 3/4" x 7" Michigan prop. This was a perfect match for the P-26. The engine ran great, and the 4 amp alternator was able to keep the battery charged. The Honda burned about half the fuel (and no oil), compared to the old Johnson.
My experience says that many people overlook the necessity for matching the propellor to their boat. It is absolutely crucial to allow engines, expecially older two-stro9ke outboards, to be able to reach their recommended maximum power at full throttle. This also holds true for mondern, high-rpm inboard diesels.
Dexter Below
Wilton, CT.
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