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Old 26 March 2014, 19:42   #1
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Newbie with newbie question.. (I think)

Me and a mate just bought a yamaha 280 sti sib, looks pretty decent has a max engine capacity of 8 though. Now we have been looking about and there seems to be lots of 6hp but with us two in the boat at all time and will only be using in the sea and not in lakes or canal this seems a bit too low? It definitely I presume wouldn't plane on that. So we looked at 8s but they don't seem very common, so after a bit of research it looks like a lot of people use higher engines than they should, so long as they don't have something that is a lot heavier and don't whack the throttle on full, it seems most people have an alright experience.

My question is, first will 10hp be ok? We will only ever be in the sea so we won't ever get to the speed we would on a still lake.

Second question will 10hp plane with 2 people on board? I with all our crap as well say 250 - 300kg?

Any replied would be appreciated.

Also.. If no to the planing question, would it be okay to stick a 15 on? Or would that be too much? (I realise insurance would be invalid)
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Old 26 March 2014, 19:45   #2
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Just re-read my message, apologies for the bad grammar I am on my phone!
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Old 26 March 2014, 19:51   #3
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Welcome to Ribnet,

Go for a 2 strokes Tohatsu 9.8 HP engine if possible to find, will work much better than any 8. It's same weight and size. Hard to tell if will plane with a 9.8 or even a 10 due to too much hull drag for that small size and passenger weight as opposed to less hull drag on larger inflatables with same HP engines. With 15 you're over powering it, how about insurance issues..

Happy Boating
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Old 27 March 2014, 02:40   #4
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Hi thanks for the response.

I will look out for a 9.8 then, though just had a look at the one u suggested and they are over a grand.. Not sure my budget will stretch that far. I am guessing a 6 hp will be too small? What knots am I likely going to get out a 8 - 9.8 on calm sea with 300 load? I estimate maybe 8-10 but as I have been reading there are so many factors.
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Old 27 March 2014, 03:25   #5
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With 300kg on board I doubt the boat will plane with a 6hp, so you will be limited to hull speed of about 6kts. An 8hp should plane with the right weight distribution and correct tube and floor pressures but it will depend on sea conditions and wind direction. A 10hp will be better, but will still be marginal with that kind of weight on board.

A lot of people over power boats and 8 to a 10 doesnt seem excessive, but I would still be concerned about transom issues and insurance. I would not put a 15hp on it (although I know some people use them on 270's) its just too much over the limit IMHO.

If you are going to overpower make sure you get the lightest 2 stroke you can ( 4 strokes are just too heavy), the Tohatsu 9.8 is a great recommendation, but as you know they are very rare and expensive. My other choice would be a Yamaha 8hp, weighs less than 30kg and bullet proof.

I think you need to except the performance limits of your boat, a 6 or 8hp will push it along very nicely, but its not an offshore power boat. There are very few days on the sea when a fully loaded 280 can plane without getting soaked, we run a 270 with an 8hp as a tender and rarely plane because its just too wet in anything but zero wind and flat calm.
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Old 27 March 2014, 14:22   #6
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Thanks for the advice.

Any members on here with experience with the larger engines for the smaller boats and how they go?
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Old 27 March 2014, 14:57   #7
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I had a 2.75m sib for fishing, this was for me and a mate, me and him 171kg, plus some light tackel two rods and a small box of gear, I started with 4.5hp merc, that was a non starter, then a johnson 6hp, no go but good on my own, then a 8hp evinrude it wouldn't get the two of us on the plane no matter what we did again on my own 18mph and great fun, so I have gone bigger to a 3.2m sib and twatsu 9.8hp, I haven't tried it out yet but praying it get's on the plane with two of us on board or my mate is gone
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Old 27 March 2014, 15:21   #8
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Haha. Can't really kick my mate out cos it will be half his boat.. Let me know how the 9.8 works for u. We are starting to look at 15s now. I cos me and my mate will have rods,gear and probably a couple of crates... Haha
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Old 27 March 2014, 16:09   #9
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Put a mariner 40 2s on a zodiac series1 a few years ago to test the engine. It was a little flighty to say the least
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Old 29 March 2014, 08:58   #10
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I'll put my hand up, I'm one of those who have used a 15hp on a 8hp rated inflatable. Boat being a sunsport 270 v air deck.

Boat was new when I bought it, started with a yam 6hp, only get on the plane with one. 11mph.

Next 9.8 merc, on the plane with 2 up and some gear. 1 up 14mph.

Then 15hp merc, same weight as 9.8, the only time it felt over the top is one up,,,,,,22mph.
Days out, 2.5 up and bits of gear very user friendly.
Only time it would not get on the plane was a wild camping trip,,,, 2 up, camping gear, food, water, refreshments, 60 litres of fuel and some bags of fire wood.

The sunsport had large tubes, inflated floor and could have a 4 stroke engine 20 kg heaver than the merc. Having gone up in engine size over some years it worked well. Had the inflatable been old, smaller tubes, dodgy transom,,,, not some thing I would have done.
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