which prop for my dinghy

X

xort

Seaman Apprentice
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Sep 24, 2006
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We're pushing a 10' RIB with a 9.8 Tohatsu 2 stroke. With one person, it gets on plane very nicely. But add a second person and conditions have to be ideal to plane off.

The prop is stamped 8.5. Is there a better choice of prop to plane with a heavy load?

Thank you
 
S

steelespike

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Apr 26, 2002
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19,069
Re: which prop for my dinghy

Thats the problem with small boats and RIBs they don't respond well to added weight.
Weight distribution may help your problem.Do you have your passenger sit well forward, Have you tried trimming the motor down(prop closer to the boat)
You would normally reduce pitch for heavy loads. Prop size is written Diameter X pitch.
Here at iboats there are 8" and 7" pitch props available.
A 7" prop, you may have to reduce throttle with a light load to keep the motopr from over revving.
Something like a Tinytach would be good to check the rpm with the new prop.
 
X

xort

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Sep 24, 2006
Messages
46
Re: which prop for my dinghy

We move weight forward as much as possible. So going to the 7" will help some? I think I'll try that. I usually don't run full out so over rev hopefully won't be an issue.
thanks
 
X

xort

Seaman Apprentice
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Messages
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Re: which prop for my dinghy

Wait a minute...

The prop was stamped 8.5 on the back side of a blade. Is this diameter or pitch? I pulled the prop off and did not see another marking inside the hub or elsewhere.
I'm thinking I'm looking at the wrong number. The props sold here show 8.5" diaand 7 or 8" pitch. So where do I look for pitch?

Thanks
 
S

steelespike

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Re: which prop for my dinghy

Seems like a reasonable approach,looking forward to your results.
 
X

xort

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Sep 24, 2006
Messages
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Re: which prop for my dinghy

Steel...are you replying to my last q? About dia vs pitch markings? Where is pitch marked?

Thnx
 
S

steelespike

Supreme Mariner
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Re: which prop for my dinghy

I was plodding along with my one finger technique. Numbers usually appear under the prop nut.
Also look carefully near the base of the blades or on the barrel.
I'm thinking the 8.5 is diameter.look carefully to the right of it perhaps masked by a coat of paint.
 
Sea Rider

Sea Rider

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Sep 20, 2008
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12,345
Re: which prop for my dinghy

8.5 is the propeller mark, stands for a 8.9 x 8.3" diam/pitch prop, will need to go for tad lower number, 7.5 or 7 mark, will need a induction tach to check, probably won't plane either, but will have better displacement speed.

Happy Boating
 
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