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Old 08-16-2018, 03:16 PM   #1
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Question Better prop for Nissan 5hp?

Picked up my dinghy yesterday. The boat planes if I sit toward the front but only gets about 6knots. Would a better prop with more pitch give me a little more speed, or is this pretty much the nature of these small engines? The prop that’s on it looks a little underwhelming. I hate to think of how slow we’ll go with two grown men on it.
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Old 08-16-2018, 03:25 PM   #2
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Actually you need less pitch rather than more to let the engine speed up, produce more power, and have some chance of getting you up on plane.


But 5 hp is really just too low to expect to plane a dinghy with.


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Old 08-16-2018, 03:26 PM   #3
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Thats probably it.

My 3.1 West RHIB does 15kts with only me and 8hp at full throttle. Back off even a few hundred and it slows quite a bit. Add another 120lbs and it will still plane just backed off from WOT.

Add 200 pounds and even getting on plane is iffy.
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Old 08-16-2018, 03:52 PM   #4
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It’s a caribe c9 and it’s rated for up to 15hp I think.

I’m not looking for kidney crushing speed, I just didn’t think it would be THAT slow. With two of us on board we could probably walk faster than it will go.
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Old 08-16-2018, 04:48 PM   #5
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It should do 5 or 6 kts ..... But at that speed for anchorages and marina's, it's throwing a pretty good wake
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Old 08-16-2018, 05:18 PM   #6
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It should do 5 or 6 kts ..... But at that speed for anchorages and marina's, it's throwing a pretty good wake
Yeah, I go just barely above an idle just to keep my wake to absolutely none. Any faster and the tubes cause more waves, albeit small, than I’m compdrtable with.

But when we cross the lake for dinner or go for a drink I’d like to get there before closing time. Lol

Maybe I’ll borrow a neighbors 9.9 and see how I like that.
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Old 08-16-2018, 05:33 PM   #7
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I had a Caribe 9' with a Tohatsu 9.9. I installed a smaller pitch prop and a Doel Fin and it would plane with 400 lbs of people and 50 lbs of dog and groceries, just fine. Before those additions it was a bit sluggish with one and wouldn't plane at all with two aboard.



Both the prop and the fin helped equally and complemented each other and let it really get up and go. But you need more hp than the 5 hp Nissan to start with, 10 hp minimum.


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Old 08-16-2018, 06:01 PM   #8
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Most dinghies are just too short.
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Old 08-16-2018, 06:15 PM   #9
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Most dinghies are just too short.
Story of my life brotha.... genetics were harsh!
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Old 08-16-2018, 07:01 PM   #10
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Fastest in our 2.6M with 5hp Tohatsu was one person well fwd using a tiller/throttle extension which gives that extra length. Two up, one person well fwd, it will plane,the person fwd gets wet if you come off the plane fast.
But,it`s a dinghy,15hp sounds a lot. Leave for dinner a little earlier, no drinking on the way.
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Old 08-16-2018, 07:54 PM   #11
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Go 9.9 if you plan to plane off regularly.
5hp is not enough unless lone imitation of hood ornament
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Old 08-17-2018, 12:18 AM   #12
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More power.... 30 hp on mine... goes faster than the mothership.
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Old 08-17-2018, 07:02 AM   #13
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Our older 5-hp outboard planed our current RIB exactly once.

That was with me and the dog aboard -- 90-lbs of hood ornament reaching over the bow -- at max throttle and suddenly (surprisingly) lifted up onto plane by the wake of a passing Sundancer going in our same direction.

Couldn't maintain that, though... the dog moved.

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Old 08-17-2018, 11:45 PM   #14
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Quote:
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I'm assuming that this 5hp is a short shaft, but not confirmed.There's a nice Nissan 9.8 for sale locally, but its a long shaft....
According to this diagram, the transom on a Caribe C9 is 17" which is right between the short shaft, and long shaft length.
So should I try it or not?
Short shaft gets you into shallower water without the prop etc touching, the water intake sucking in sand and damaging internals, etc.
It`s early, plenty of spending to come,to try it you likely need to buy it,stay with what you have for now.
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Old 08-17-2018, 11:47 PM   #15
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Short shaft gets you into shallower water without the prop etc touching, the water intake sucking in sand and damaging internals, etc.
It`s early, plenty of spending to come,to try it you likely need to buy it,stay with what you have for now.

You replied before I deleted my question. LOL

I found a reputable site online with good information. I'd likely have to raise a long shaft off the transom a few inches to reduce drag.

So I'm sticking with the 5 for now.

(I'm really just bored while working nights so I'm doing my obsessive researching thing.)
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