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Catalina/Capri 25/250 Sailor's Forums

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High Thrust Prop Dimensions

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Initially Posted - 12/20/2002 : 14:49:52

I contacted Michigan Wheel about prop selection for my motor and they have props from 9 1/4 x 7 through 9 1/4 x 12.

I'm considering the 9 1/4 x 7, but my question for those with high thrusts props is,...What is the dimensions of your prop?

Thanks

Don Lucier, 'North Star'
C25 SR/FK
On the hard, 200ft from Lake Erie

Edited by - dlucier on 12/20/2002 14:51:02

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Derek Crawford
Master Marine Consultant

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USA
3324 Posts

Response Posted - 12/20/2002 : 16:46:01

Don - I have a Nissan 8 h.p. and have just bought an 8.5 x 6.5 prop for it. The original was an 8.5 x 7.5 and the new one gives much more manoevrability at low RPM's. Nissan told me that at cruising speed it will increase the rpm's by about 200.
Derek

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 12/20/2002 : 17:57:19

Don: The Honda Power Thrust 8 and 9.9 have 10" x 6.5" props. The lower pitch is partially offset by the larger diameter, but you probably can't go that large, so 7" pitch sounds good. What is your current prop?

Michigan Wheel should be able to make a recommendation based on your displacement, hull speed and engine... Did you try their "Prop it Right" feature on their Web site?

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

Edited by - Dave Bristle on 12/20/2002 18:05:18

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 12/20/2002 : 18:51:29

Derek and Dave,

Thanks for the info. I'm not exactly sure what size my current prop is. The diameter is 9" when measured with a tape, but I don't really know about the pitch. The prop is stamped with a "9P" and a "12". Could that mean it's a 9" x 12"?

Yes, Dave, I did use the "Prop it Right" feature, but the questionaire leaves out an important question, specifically "Hull Type". I would think that knowing if the boat is a planing or displacement hull would be kind of important?! Anyway, at the end of the questionaire there is a box for further explanations in which I detailed my needs in a prop/motor. They emailed me this today,

"This is kyle from michigan wheel. we have 9 1/4 x 7 through 9 1/4 x 12. We also have straight 9 diameters ranging in pitch between these two sizes. if you have any more ?'s or concerns call or write back"

I'm going to contact Mercury marine to see what they recommend for my motor. Their website is a little lacking in this area.

Don Lucier, 'North Star'
C25 SR/FK
On the hard, 200ft from Lake Erie

Edited by - on

Arlyn Stewart
Master Marine Consultant

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USA
2984 Posts

Response Posted - 12/20/2002 : 19:55:39

One point that Dave didn't mention about the Honda 10 x 6.5 prop is that it is a four blade.

<img src="http://www.cox-internet.com/arlynstewart/images/helming.jpg" border=0>
Arlyn C-250 W/B #224
R&R N/E Texas and Great Lakes

[url="http://www.cox-internet.com/arlynstewart/"]Arlyn's C250 Mods n Cruisin Stories[/url]

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 12/20/2002 : 20:13:22

Don: If your pitch is 12, it's a very sharply pitched prop designed for something like a small inflatable that planes. In that case, you're going to be amazed by the difference with a 7" pitch. The 12 is designed to "pull" a boat through water much like a screw goes through wood, which means the boat must be moving very fast. The 7 is designed to throw water from stationary or slow-moving position, providing "thrust." That's us--slow moving, and we need thrust to start and stop our 5000+ lbs.

Go for the 7--as Derek says, you'll hear the engine rev up a little more at cruising speed, but working around a dock, you'll be amazed by the pushing power.

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 12/20/2002 : 20:42:35

I'll probably go with the 7" pitch prop, but I still want to talk with Mercury about performance issues. Also, on your Honda is the prop the only thing that makes it a "high thrust" model or is the gearing in the lower unit different as well?

Don Lucier, 'North Star'
C25 SR/FK
On the hard, 200ft from Lake Erie

Edited by - on

Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 12/20/2002 : 21:54:36

Honda's site says the gearing is 2.33 for either the standard or Power Thrust version. That ratio could be somewhat different from the ratio for a 2-stroke because the torque curve is different. As I said, you'll get a little higher RPMs at cruising speed with the lower pitch prop, but that's the price for having the push at 0-1 knot. (Maybe some day they'll make a 5-speed gear box or a variable-pitch prop.)

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

Edited by - on

Gary B.
Admiral

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USA
969 Posts

Response Posted - 12/22/2002 : 23:27:33

Just for grins, I looked at the prop on the Yamaha 9.9 high thrust that I am often raving about. It works great on the low end, plus, it pushes my boat way beyond theoretical hull speed if I open her up. I always thought the prop looked huge. It is an 11 3/4 X 9 1/4. It swings 3 big blades, not the 4 of the Honda high thrust.

Gary B.
Encore! #685 SK/SR

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dlucier
Master Marine Consultant

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Virgin Islands (United Kingdom)
7583 Posts

Response Posted - 12/23/2002 : 09:30:42

Wow, 11 3/4"?...That's a good size...for a ceiling fan? <img src=icon_smile_wink.gif border=0 align=middle> You must have the thrust of a tug boat!

Don Lucier, 'North Star'
C25 SR/FK
On the hard, 200ft from Lake Erie

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Dave Bristle
Master Marine Consultant

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Djibouti
10005 Posts

Response Posted - 12/23/2002 : 20:30:11

<BLOCKQUOTE id=quote><font size=1 face="Verdana, Arial, Helvetica" id=quote>quote:<hr height=1 noshade id=quote>
Just for grins, I looked at the prop on the Yamaha 9.9 high thrust that I am often raving about. It works great on the low end, plus, it pushes my boat way beyond theoretical hull speed if I open her up. I always thought the prop looked huge. It is an 11 3/4 X 9 1/4. It swings 3 big blades, not the 4 of the Honda high thrust.
<hr height=1 noshade id=quote></BLOCKQUOTE id=quote></font id=quote><font face="Verdana, Arial, Helvetica" size=2 id=quote>
That's interesting... I see on their site that the drive ratio is 2.92, which probably compensates for the higher pitch than the Honda. But I'm still surprised the pitch is that high. The diameter compenstates for the number of blades.

Dave Bristle - 1985 C-25 #5032 SR-FK-Dinette-Honda "Passage" in SW CT

Edited by - on

Gary B.
Admiral

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USA
969 Posts

Response Posted - 12/24/2002 : 15:03:05

Don: It DOES have the thrust of a tugboat. My old 1985 model which I have now replaced with a new one, once towed a 28 foot Bayliner into Friday Harbor several miles against a current. We were only making 3-4 knots which made him a little crazy, but we got there. The powerboats out never stopped to render assistance. I loved the picture of he C25 towing in a much larger stinkpotter. I am not kidding; I am a real fan of this engine. I haven't tried the newer, high thrust Hondas, but I'd be really surprised if they pull any harder.

Gary B. Encore! #685 SK/SR

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