Prop Matching on a Honda Outboard

[mark_turner]

My friend has just bought a 20ft , 1.2tonne (with engine and gear) river boat which came with an old 9.9hp Honda.

The propellor on the engine is a bit the worse for wear and so we rang Honda themselves who put us on to their recommended Honda dealer near to us and asked what prop we would need.

Regrettably they did not inspire confidence, resorting to "What has it got on it at the moment?" then, when I said that I didn't know "Bringi it in and we'll get one to match" . All well and good but what if it is the wrong one? Surley if the 'standard prop' was supplied when the motor was new, it is not likely to be appropriate for a very heavy slow boat?

Would it not be a simple task for Honda or whoever to work out a standard table listing such things as Engine model, hull type, boat displacement and what ever else it depends upon and in each box put a number of suitable props to choose from.

If it is not this simple, is there perhaps a simple way of calculating which prop woud be best for this boat?

In the meantime I am going to try a few more Honda dealers in the hope that they might be more helpful.


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[aztec]

might be talking out of turn here but, you may not have much choice in the way of props for an off the shelf engine. as you would with a fitted package out drive, or high output engine.

cheapest is to get a 2nd hand prop, get it repaired/repitched and try it. after all would the prop make much difference, 10hp on a 20ft river boat? it's going to be somewhere handy.

all the best, steve.


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[mark_turner]

Thanks for this.

A bit more research shows that you are correct in that there is not much choice. Only two props made for this engine - on at 9 1/2 inch pitch and theother at 8 5/8 inch pitch. We are going for the finer pitch and, as we wouldn't have anything to compare it with, will no doubt be quite happy with the result.

Mark

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[Chris771]

Mark

Back in my days of canalling about 10-15 years ago I had a Norman 20 and a Buckingham 22, both with 10hp Honda engines.

Originally they both had the standard propellor. As I often visited the USA with work at the time I bought the finer pitch propellor offered by Honda and brought it home and fitted it.

The nett result was a few more revs, noticeably quicker accleration and noticeably greater fuel consumption due to the higher revs. The boat did not go any faster (maybe 1/4 knot but but no more) but just made more noise and used more fuel. After a while I went back to the origianl propellor. I tried the finer one on both boats with the same effect.

As Steve says, I would be inclined to stick to the standard propellor, with 10hp on a relatively heavy boat you are not going anywhere at above displacement speed around 5 kts if you are lucky, so you may as well run in the equivalent of 5th gear nice and quietly rather than scream along in third making more noise and burning more fuel to no useful effect.

Obviously for maximum efficiency on a small planing dinghy you would prop to achieve maximum revs and maximum planing speed. But on your boat it will only make more noise - not go any faster.

Regards

Chris

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