Honda 90 Propellor

[savage]

I'd really appreciate hearing for other members what props they are running on their Honda 90's.

I've currently got a 13 3/4" x 15 pitch and I think it's not the right match.

Current stats

MAX RPM 5,800

Max speed 46Kmh

My boat is a Savage Osprey 5.25 200 year model, not a heavy boat and I would of thought I should be getting more top end speed. The main concern is I'm having to sit on approx 4500 rpm to curuise at 18knots which seems too high for this type of boat.

Any feedback would be greatly appreciated.

Thanks,

mike

[fryboy]

Oh man, I'm just going through the same thing, but different boat and motor. Actually just ordered a new prop from the states this week to try and improve performance.

My research has found:

To really know your problem, you need to know the engine manufacturers recommended max rpm, then work from there. You need to test on some flat water (thats good fun ..) and should get near that max rpm at WOT with a normal load in the boat and trimmed for the conditions. If you are not getting there, you should down pitch on the propeller, otherwise your engine is working harder than it needs to to get you up on a plane and keeping it there. Each inch of pitch relates to about 300rpm I'm told.

For example, my engine was maxing out at 5300 rpm, thats 700 less than the 6000 max recommended by Yamaha for that engine. I am running and 19 inch pitch, so the theory would be to go to a 17 inch pitch. However.... then it gets interesting, because different props offer different performance. For example, the prop that I've ordered has more cupping and a higher rake angle (yeah, I dont know either), so the manufacturer has recommended a 15 inch pitch for me.

From a lot of reading, I can tell that its a bit hit and miss. Even though this 15 inch propeller I've ordered looks like the ducks guts and sounds it too, I might put it on and get worse performance. So lucky that the manufacturer is ok to swap if not ok (but the postage to and from the states might kill me). So whatever you do, dont buy a propeller without testing it or having the option to switch.

Just as an aside, I ordered the prop from the states because its much cheaper due to the dollar (go you aussie, go). The same Solas prop in Australia is $650, but even with postage from the states, I've got the same prop for just a tick under $400. (PM me if you want details on where I got that propeller from. )

Hope this helps. Key thing you've got to do is find that max rpm

Fryboy

[fryboy]

Oh, and the other thing thats critical - check the engine is mounted at the right height. To do that, get the thing going at WOT and nicely trimmed, then check that your cavitation plate (wing/flange just above the prop) is skipping along just on top or just barely in the water. (Top tip from Fryboys boat driving skills course - get someone else to drive while you check the cav plate!)

Bad motor height can affect the performance more than a bad prop apparently.

Fryboy

[spic]

Thanks for the replies guys.

I did the motor height last year and got that right.

I know everyone talks about the picth but what impact does the diameter have? Been searching around and most of the references are to the pitch not much on the dia.

Edited October 14, 2010 by spic

[fryboy]

Hi,

You dont get a lot of choice with the Diameter. As the pitch increases, so does the Dia. There was only about .5 inch difference in dia among all the 15 and 17 inch props that I was looking at.

Heres a great article on propeller technology if you have the time.. http://turningpointpropellers.com/propellers_101_cm.htm

fryboy

[tuffy]

Fryboy, the diameter is not that relevant, it is the pitch which has the most bearing on performance. I've just been through this with Honda for my 50hp. Unfortunately Honda supply their standard props as a generic, in other words it is designed for an average boat etc, but we all know that every boat differs in use, design, hull shape, general load etc, so it really becomes a very individual situation. I finally got mine right with the superb assistance of Steve Evans at Solas props in Brissy. Basically sold me the initial prop and exchanged free of charge later when the boat wouldn't perform properly.

My recomendation would be to talk to Solas- they are extremely helpful - and tell him your probs. Your Honda 90 has a max rev range of 5300rpm to 6300rpm and a max HP at 5800 rpm, so it sounds to me like you are close to within that range. The original prop is ally and they are not very well designed. If you went to a stainless prop of the same pitch they have a vastly different blade shape from the Honda prop and you will enhance your performance substantially. Talk to Solas, they are the experts in this country. Don't make the mistake of importing from the States as there is no exchange facility and the few bucks you save may not be worth it in the long run.Besides, I like to support Aussie business. Make the call, you may well be surprised.

Cheers, Tuffy