Honda 5hp outboard

[PhilipH]

Couple of questions for the panel:

1 we get quite a bit of cavitation when on the plane (yup, checked the angle and also throttle back a bit) and thinking about fitting plastic hydrofoil/Doel type fins - has anyone experience of these, please? http://cgi.ebay.co.uk/SMALL-MOTOR-H...vr_id=&cguid=efea0c7b1280a0e204416ec1feb4ef51

2 has anyone used this Seloc service manual http://www.amazon.co.uk/Honda-Outbo...=sr_1_2?ie=UTF8&s=books&qid=1280423077&sr=8-2 - does it mean not paying huge service costs?

Oh yes and 3 - just what is the right way for putting a link in thread?

 

[VicS]

3. what you are doing is quite accetable but use the insert link icon:

, paste in your link hit OK and then type in the words you want to appear in your post.

2. 3rd party manuals tend to cover to many models from too many years and can as result be deficient in fine detail just when you need it most. Manufacturers manuals are infinitely better and more model specific but considerably more expensive.

1. Do you really mean cavitation, which is when the prop "loses it grip" so to speak on the water or do you mean ventilation which is when air is drawn down into the prop.

If the later the engine may be mounted to high. The anti-ventilation plate above the prop should be roughly in line with the bottom of the transom. Doel fins might help

If you really mean cavitation then your prop, engine and boat are badly matched to each other. Doel fins wont help

 

[PhilipH]

Hm

now, not sure whether it's cavitation or ventilation (until you mentioned it I had never heard of the latter!). Symptoms are that when dinghy (3.1m Avon Rover Aero) is on the plane, then the engine will over rev and the boat will slow down. It all becomes a bit jerky. The engine is the standard shaft i.e. not long shaft, and as low as it will go without cutting a chunk out of the transom.

 

[VicS]

Very probably ventilation but my first reply contained just about my total knowledge of the subject. Not an area of great interest to me I am afraid.

I offer you THIS LINK for what its worth. ( I note in there they refer to the AV plate as an anti-cavitation plate )

The plate can be up to about 1" below the bottom of the transom but the lower you go the greater will be the drag.

Your owners manual should give you information about mounting the engine. I note they say the plate should be 2" below the bottom of the boat ... so conflicting advice there from different sorces!

If yours is much above the bottom of the transom then it could be your problem.

I assume you have a 10hp engine being the max recommended for the boat. Avon don't seem to say what shaft length is required although I'd have thought short(aka standard) shaft engine would have suited.
I notice that Hondas quote shaft lengths a couple of inches longer than other makes being approx 17" for the short shaft instead of 15" and 22" for a long shaft instead of 20" But I think that may be a slightly different way of measuring

I can't some how think you have a problem with shaft length. your Honda may in fact be a little longer than ideal. You can but look at the motor when on the boat.

Perhaps if deep it is tending to lift the bow.. More weight in the bow any help perhaps.

 

[PhilipH]

Very many thanks

and I see you have achieved "Forum Stakhanovite Hero, 1st Class" status! Congratulations