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Old 16-06-2012, 07:24   #1
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Small rib 15hp how fast?

As the title says - 3M ish rib with 15hp , how fast?

Managed 21kn with an 8hp 2 stroke, boys will be boys

Thinking of either upgrading to15hp or a 9.8 tohatsu 2 stroke as my current 8hp is bloody heavy 34kg so if im going for a crane id go with a 15hp but if fast enough the tohatsu 9.8 2 stroke is 26 kg manageable without a crane.
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Old 16-06-2012, 07:27   #2
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Re: Small rib 15hp how fast?

I tend to overpower my dinghies not so much as to have a racer, but still be able to plane off with 4 adults. My favorite was an 11' Whaler with a 40 on it.... Had to dip my hand in the water to wet my hair every so often to put out the fire!
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Old 16-06-2012, 08:11   #3
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Re: Small rib 15hp how fast?

Not sure that upgrading from an 8hp to a 9.8hp is a major difference. 15hp on the other hand will be night and day from a 8hp. I have a Merc 5hp 4 stroke and a Tohatsu 18hp 2 stroke. The 5 is fine for checking in, groceries, sips the gas, and for general poking around near the big boat. But the 18hp takes me far and wide. I like to dive and explore and the 18hp fits the bill a lot better. Also, and I've never had the need to, the 18hp is a nice auxiliary if the main engines ever fail on my Cat.
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Old 16-06-2012, 08:32   #4
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Re: Small rib 15hp how fast?

With the 9.8 it is more the weight than power issue the 9.8 is 26kg, man handleable, while my current 8hp is 34 kg, doing my arms in, hence the need for a change, so if i go for the crane idea then id go bigger to the 15hp, without the crane it will be the 9.8hp, so maybe the question should be is a 15hp worth the effort of a crane and extra expense over a 9.8 hp? Nb any speed figures for a 15hp on a small rib, actual numbers, out of curiosity?
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Old 16-06-2012, 08:42   #5
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Re: Small rib 15hp how fast?

I don't think it will be worth the effort and expense for the 15hp if your current 8hp works well. At some point, the dinghy handling will get squirrely and dangerous with too much power. We have a 15hp on a 3.7M (12') 350lb deep hulled RIB and with one person on board, it gets squirrely at WOT. I couldn't imagine it on a 3M dinghy.

On the other hand, if you are regularly hauling a lot of people or equipment, the 15hp will be good.

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Old 16-06-2012, 08:53   #6
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Re: Small rib 15hp how fast?

There is another choice when the time comes for a new dinghy. Light (17.5 kg for motor, 30 kg for dinghy) fast due to easy planing of an air entrapment catamaran hull. The dinghy HOME - Takacat.com the motor Cruise T mit Pinne||Dinghies, Segelboote, Motorboote bis 4 t
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Old 16-06-2012, 09:18   #7
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Re: Small rib 15hp how fast?

Quote:
Originally Posted by capngeo View Post
I tend to overpower my dinghies not so much as to have a racer, but still be able to plane off with 4 adults.
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Old 16-06-2012, 10:06   #8
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We have a 3.1m rib with 15 on the back and in flat water it goes like crazy, but in anything other than flat it is rare we can open the throttle without scaring the admiral or bouncing baby crew out over the side. Where we find it really helpful is when we have four adults, fuel, water groceries etc....

...that and me and the lads jamming out for a bit of fishing with the admiral and crew left back on the boat
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Old 16-06-2012, 10:25   #9
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Re: Small rib 15hp how fast?

Wow... how did they get a 9.8 HP down to 57 lbs!
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Old 16-06-2012, 10:40   #10
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Re: Small rib 15hp how fast?

I sailed from San Francisco Bay to the Sea of Cortez (and back) with my wife and two teenagers. We have an Achilles RIB that weighs approximately 205 lbs. (92.9 kg) empty, and a 25hp, 2-stroke that weighs 114 lbs (51.7 kg). The fuel weighs another 35 lbs. or so (15.8 kg). It was a pain in the butt to manhandle the dinghy from the foredeck over the side using the halyard to raise and lower it, but it was worth it! I tried using a halyard to raise and lower the outboard, but it was easier for me to just lift it and carry it myself. I finally bought a crane, but it's not installed yet. Other than the difficulty launching it, the two drawbacks I found were;
1. It used a lot of fuel, and
2. It was very difficult to pull it up the beach far enough.
The benefits included;
1. It was very fast, and never failed to plane no matter how many people (up to 7 adults) or how much stuff was in it. (planing really kept the splashing down)
2. It increased our ability to travel and explore in the dinghy.
3. It opened up our anchoring choices, for example, at Cabo San Lucas, we anchored over a mile away from the harbor entrance, away from the noise of the bars and away from most of the jet skis.
4. We were able to tow people on surfboards.
5. It was fun!
6. Did I mention that it was VERY fast?
I believe that the ideal tender for me is two dinghies, one like the one I have, and a small one that either rows well, or can be sailed, or both.
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Old 16-06-2012, 10:53   #11
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Re: Small rib 15hp how fast?

Hi,

have an AB Lamina, 9ft with a 9.8 HP 2 stroke - goes almost 20 knots as well. My tohatsu says something like 26kg - I guess your 8HP must be build like a tank

I love my combo, but yes I would go longer with the dink but there was no room on deck because of the staysail.
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Old 16-06-2012, 11:08   #12
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Re: Small rib 15hp how fast?

I don't know about any 4 strokes but at least with many 2 strokes the 9.9 is just a detuned 15. Same weight.

Some have taken their 9.9 and changed the carb and exhaust to get the 15 as well.

I tend to go for 11' tenders currently with a 9.9. This gives around 20 kt with just me and 17 with the 3 of us.

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Old 16-06-2012, 11:46   #13
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Re: Small rib 15hp how fast?

One more vote for the 15hp if you want to plane with 4 people--the 9.8 should be able to handle 3 people, and the 8 should plane 2 (unless they are overweight).
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Old 16-06-2012, 11:58   #14
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Re: Small rib 15hp how fast?

hey you calling me fat, im just big boned I like the idea of the 9.8 it saves any crane and less power is less thirst after all, the little 6hp four stroke i have just sips fuel so lightly its great for pottering about any ideas where to get a 2 stroke tohatsu in the med? eu countries are nigh impossible.
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