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Catalina/Capri 25/250 Sailor's Forums

Catalina 25 Specific Forum

Yamaha 9.9 high thrust

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Harleyworker
1st Mate

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USA
73 Posts

Initially Posted - 08/26/2010 : 11:38:34

I just bought a 1997 yamaha 9.9 four stroke, and I absolutly love it. I had a mariner 9.9 two stroke that I called my two cylinder diesel, because that's how it ran. The new motor is soo quiet I almost forget it's running at idle. It pushes the boat fantastic and will actually pull the bow up at any throttle position. The only thing I noticed is I'm getting hull speed at about half throttle, so I was thinking I should/could change out the prop to help the motor out and use the power range better. I haven't checked what prop is on there, it's factory. Has anyone with this motor changed their prop and what did you go with?

Harley
1979 C25 tall/fin
Hull# 1246
"Mein Engel"

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GaryB
Master Marine Consultant

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USA
4303 Posts

Response Posted - 08/26/2010 : 17:32:44

Most outboards have a max RPM range say 5000 - 5500 RPM. Whatever prop you use should allow the motor to run in that range at full throttle. I've heard that it's slightly better for the motor long term to let it turn in the upper range as close to the redline as possible.

The deeper the pitch the slower you will accelerate and the more stress it puts on the motor while accelerating. You will eventually reach a higher top speed (maybe) but it will take longer.

The ideal prop allows you to accelerate at a nice pace without lugging the motor, turn at the proper RPM when at full throttle, and get the best gas mileage possible.

Edited by - on

Jmurfy
Navigator

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USA
176 Posts

Response Posted - 08/31/2010 : 20:57:36

I used my 1998 Yamaha 9.9 to motor diagonally across Lake Michigan from Douglas, Michigan to Chicago. About 110 miles. Great reliable motor.

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Brian Clancy
Deckhand

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8 Posts

Response Posted - 09/12/2010 : 09:23:44

Jmurfy, do you remember what gallons-per-hour you observed on your trip? I just purchased a 85/Tall/Fin (will create another post) with an older 9.9 Yamaha.

Also, the tiller behaves calmly when sailing. But when motoring at high (5-6) speed, it was like a wresting match. Anyone else observe this?

Brian

Edited by - Brian Clancy on 09/12/2010 09:24:15

Dave5041
Former Mainsheet Editor

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USA
3758 Posts

Response Posted - 09/12/2010 : 10:16:29

The problem is that we mostly get 9.9's because that is the smallest motor with the feature set/price that we want. It is a lot more HP than we need. Extra HP doesn't help with a displacement hull - we could probably do fine with 4 HP spinning a flat prop @ 5000 rpm - speed is set by the hull and cranking the throttle just makes the stern squat. I don't believe that you will significantly impact fuel economy or any other parameter enough to make it worthwhile.

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John Russell
Master Marine Consultant

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USA
3444 Posts

Response Posted - 09/12/2010 : 10:45:07

Another reason for the 9.9 is that 10HP and larger motors have to be registered and incur a registration fee separate from the boat. You will also pay taxes on the amount that the motor was purchased. At least, that's the way it is in Ohio. I assume that's true in most places since all the manufaturers build/sell motors at just a hair's breadth under 10 HP.

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Stinkpotter
Master Marine Consultant

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Djibouti
9076 Posts

Response Posted - 09/12/2010 : 13:39:34

2-cycle engines are happy near the red-line (chainsaws, weed-eaters, etc...) 4-strokes run more comfortably well below that (like your car). Our Honda 8 ran between half and 2/3 throttle to get 5 - 5.5 knots--the most efficient speed in our experience. I suspect a higher pitched prop could have given us a little better mileage by dropping the RPMs a little, but I had such a prop on the engine that came with the boat, and the difference in low-speed thrust for maneuvering with the high-thrust (lower-pitch 4-blade) prop, particularly in reverse, was dramatic.

If you have Yamaha's "High Thrust" model, you have a similar prop--three blades, larger diameter, and lower pitch than standard, which should behave about the same as ours. Going to an even lower pitch (for higher RPMs) would just burn more gas and make more noise to go the same speed. The "standard" prop is for pushing light, planing hulls to planing speed--the high-thrust prop is for displacement hulls at lower speeds.

Edited by - Stinkpotter on 09/12/2010 13:45:36

sonofasailor55
Deckhand

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USA
2 Posts

Response Posted - 09/12/2010 : 14:22:37

I think your selection of a 9.9 Yamaha 4 stroke is a good one. I just put a Honda 9.9 on our boat and have much more confidence in our ability to deal with adverse wave and wind conditions. Our previous Evinrude 4 hp two stroke was a bit underpowered for a boat of this weight in high waves and wind. Our Honda, with high thrust prop, delivers great fuel economy and performance in the mid to 3/4 rpm range. Like you highlighted, the quiet operation of the 4 stroke is wonderful.

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dmpilc
Master Marine Consultant

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USA
4593 Posts

Response Posted - 09/13/2010 : 08:37:49

We have the Nissan 9.8 XXL electric start and I love it. I would have preferred the 8 hp model (a little less weight and cheaper), but couldn't get it with both XXL and electric start. Although the electric start was for the admiral, I really enjoy it myself as well. Like your Yahama, the Nissan is very quiet.

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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.