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Old 15 May 2022, 08:14   #1
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Yamaha 5hp prop

I'm very happy with my 2 stroke Yamaha 5hp.
It's nice and light and I get about 13mph on fresh water wot. However, on the odd occasion when I have a passenger it drops down to displacement speed.
It would be pointless for me to sell it just to improve performance for the few times I have a passenger so I was wondering, for these occasions, if there is an alternative prop I could use to increase performance slightly......or not
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Old 15 May 2022, 08:45   #2
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It's the usual answer Tommy. You need a £10 rev counter to see what the actual revs are at these speeds... and to know the existing prop pitch.

But from experience with something around a 5hp getting on the plane is often only when one-up anyway.
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Old 15 May 2022, 13:05   #3
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I have zero knowledge about props
When I have a passenger the engine definitely doesn't reach it's normal maximum revs.
So I'm presuming, like a dropping down a gear on a hill, if I put the next size lower on it, it will be able to rev higher but not quite reach it's normal speed but a better speed.
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Old 15 May 2022, 13:07   #4
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This is what I have
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Old 15 May 2022, 15:46   #5
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I can't quite decide what that says. I think it should be 7.5"dia x something... but the something seems to have a 7 and 8 plus something else?? Either you'll be able to see or a really sharp image would help. I think there is a 7.5 x 7BA (being a 7" pitch) and it could be that??

Anyway the pitch sizes are often 7" or 8" for that outboard so you may well be on the lower one of those usually fitted. I did a quick search and couldn't find anyone offering a 6" pitch but there is a 7.25" x 6.5" however not sure 0.5" pitch reduction will make much difference.

In any case it could be you are hitting the barrier of physics in that a 5hp will not plane your SIB two up. The only further investigation would be as I mentioned to get a cheap tach and see what he revs are doing when you are flat out one up and bogged down two up.

If you do have a 7" pitch and wanted to try a 6" but none available off the shelf then a prop shop like Steel Developments can re-pitch your existing prop or a new one they supplied.

I note also there is a 6" pitch prop for the smaller Yamaha 2-strokes but no idea if this would fit.
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Old 15 May 2022, 16:48   #6
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Yeah it could be 7BA.
It's still Chinese to me, I'd be grateful for a layman's explanation on gradings
As you say it's probably never going to plane 2 up anyway, it's just that I watched a YouTube video of a tohatsu 6hp speed test and in the description he says he has changed the prop, lost 2mph top end speed but gained being able to plane 2 up
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Old 20 May 2022, 17:02   #7
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Managed to borrow a 7ľ X 6Ĺ. .
Dealer said it is compatible with mine .
Big difference in appearance
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