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Old 01-03-2015, 15:41   #1
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Soft dinghy to RIB

I own a 9.8 outboard, on a West Marine 310 inflatable, with wood floor.

Wife and I are bulky, and it will not plane off, unless we move way foward.

Since I am thinking about buying a new RIB anyway, will the same engine and prop, on a 310 RIB, plane off easier

Just wondering if anybody has done this

Go ahead, I can take it.

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Old 01-03-2015, 15:52   #2
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Re: Soft dinghy to RIB

Depending on the age of the outboard, re-jetting it could increase your hp. Don't know if it will plane you guys or not. How much weight are we talking about.

FWIW, our 15 hp will plane ~ 600 lbs., on a 3.5 m. alloy RIB, but not into a strong head wind (20 k.). Sometimes adding a planing fin will help; also, changing props can help, too.

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Old 01-03-2015, 16:35   #3
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Re: Soft dinghy to RIB

I've found that most people are unhappy if they expect to plane a boat and put less than about 60% of the boats rated hp on it. If the RIB is rated to take more than 15 hp, you will be unhappy with the 9.8. If it is rated for 15 hp, you might be ok with a 9.8 but you'll be happier with a 15.


I recently finished building a little plywood skiff from plans. It is rated for fifteen hp and I was planning to put a 9.9 Lehr propane engine on it. By the time it was finished, Lehr had come out with a fifteen so I went for that. I don't regret it. The boat jumps onto plane with two big guys aboard.
Now LEHR has come out with a 25, I wonder? Naw, I better not.
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Old 01-03-2015, 16:48   #4
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Re: Soft dinghy to RIB

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Originally Posted by Ann T. Cate View Post
Depending on the age of the outboard,
Quote:
Originally Posted by Ann T. Cate View Post
re-jetting it could increase your hp. Don't know if it will plane you guys or not. How much weight are we talking about.
...Ann
Ann makes a good point. Frequently, the only difference between a 6 and an 8 hp, or a 10 and 15 horsepower motor, are a couple minor parts. Certainly worth talking to a local outboard shop before buying a new motor.
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Old 01-03-2015, 17:28   #5
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Re: Soft dinghy to RIB

Another suggestion is to use a finer pitched prop. Your top speed will reduce but your planing load capacity will increase.

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Old 01-03-2015, 17:50   #6
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Re: Soft dinghy to RIB

I got all the prop pitch, bigger carb stuff.
The dink I have, is rated for 10 hp. The motor is 2 years old.

Just wondering if a same length RIB, planes easier.

Thanks

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Old 01-03-2015, 17:55   #7
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Re: Soft dinghy to RIB

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Originally Posted by twinboat View Post
Just wondering if a same length RIB, planes easier.
Yes.

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Old 01-03-2015, 19:04   #8
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Re: Soft dinghy to RIB

You might want to check out this link. http://commutercruiser.com/why-wont-my-dinghy-plane/


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Old 01-03-2015, 19:14   #9
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Re: Soft dinghy to RIB

It was my rather lengthy historical account on the link cited above on why our fiberglass roll up 8 foot Caribe dinghy wouldn't plane with an 8 hp outboard. Bottom line - read the history of what we endured to find out from Defender Industries that the reason our dinghy wouldn't plane was because our Caribe foot pump was not capable of inflating the tubes enough to plane. Ask us how skeptical we were about this diagnosis - NO WAY! Our tubes felt rock hard to us ... but in desperation we followed Lance at Defender's instructions and voila our 8' roll-up Caribe dinghy had no trouble FLYING.
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Old 01-03-2015, 20:07   #10
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Re: Soft dinghy to RIB

Some people have had success with adding planing fins to the outboard. Depending on cost for your motor I would try that first.

Also, I know you said you are "bulky" but 10hp is a lot of hp for two people (OK maybe not in these days of excess) but sitting two big people at the rear is a bit optimistic.
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Old 02-03-2015, 02:56   #11
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Re: Soft dinghy to RIB

OK, next ride will be with a freshly pumped up dinghy. I`ll post results.

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Old 02-03-2015, 04:21   #12
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Re: Soft dinghy to RIB

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Originally Posted by twinboat View Post
I own a 9.8 outboard, on a West Marine 310 inflatable, with wood floor.

Wife and I are bulky, and it will not plane off, unless we move way foward.

Since I am thinking about buying a new RIB anyway, will the same engine and prop, on a 310 RIB, plane off easier

Just wondering if anybody has done this

Go ahead, I can take it.

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Ive owned over 6 ribs over the years, its very hard too min/max the rib weight/length/ engine size and come up with a good planing RIB

The best I had was a 5 m with 170Hp, the worst was a light weight rib with a Johnson 9.9

personally I think you have to start exceeding 15hp, to get a good all rounder that can handle any sort of chop, weight imbalance, or headwind. and 15hp is really the upper limit of manual handling outboards.

You may have too accept that you cannot meet all your requirements

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Old 02-03-2015, 05:56   #13
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Re: Soft dinghy to RIB

And you do need to think about weight when dragging the tub up and down the beach.

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Old 02-03-2015, 06:24   #14
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Re: Soft dinghy to RIB

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personally I think you have to start exceeding 15hp, to get a good all rounder that can handle any sort of chop, weight imbalance, or headwind. and 15hp is really the upper limit of manual handling outboards.

Back to that 99 lb, 20 HP Suzuki, same motor as their 15, same weight.
I think other manufactures, have or either will soon have 100 lb 20 hp motors.
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Old 02-03-2015, 07:27   #15
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Re: Soft dinghy to RIB

I too am looking at going the RIB option. We have a new West Marine wood floor inflatable keel dinghy as well and run a 9.9 4 stroke on it. With me, the wife and our two boys (450lbs. total weight) it take a long time for us to plane out but it is possible if we move our weight around. Once on plane we scoot at about 18kts.

We borrowed a friends 310 RIB and used our 9.9 and we got on plane with no issue.
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