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Old 19 March 2009, 23:31   #1
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Can you plane or get up on top of the water with a flat bottom sib?

Hey im still deciding between a flat bottom sib with slatted wood floor or a sib with an inflatable keel and plywood floor.

My question for you is, can you still plane and get up on top of the water with a flat bottom or do they kind of just drag themselves in the water.

I will be using a 6-10 hp motor, not sure yet.

Im getting a way better deal on the flat bottom so its a really tough decision.

Thanks guys and im sorry for all the dumb questions. This is just a lot of money for me so its important.

Ryan
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Old 20 March 2009, 02:50   #2
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have a look at this -

So yes flat bottoms do plane, although I prefer a curvy one

how big are the boats that you are looking at?
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Old 20 March 2009, 02:59   #3
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haha thats awesome. I dont think i worded my question very well. Im only looking at 3 meter SIB's but what I was trying to figure out is can you still plane with a short little flat bottom. I guess i was just trying to figure out if you have a little 9 foot sib with a 10 horse motor on it can you sill plane and go fast up on top of the water.

If you have one with a slatted roll up floor that is flat bottom will you get destroyed if you hit a wave going full speed?

Haha i know these questions probably seem dumb to you guys but i've never even rode in one of these thigns so im trying to figure it out before i buy one.
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Old 20 March 2009, 05:39   #4
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our club sec in his flat bottomed sib with a 4 hp engine , it will plane one person as long as the weight is well forwards.
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Old 20 March 2009, 05:44   #5
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what about with some extra weight in the front like a beer cooler or another person?
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Old 20 March 2009, 06:16   #6
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what about with some extra weight in the front like a beer cooler or another person?
with a bigger engine yes but for a small engine like the 4 hp in the pic you need as less weight as you can have on board, in the pic he needed to sit further forwards but he dident have a tiller extention with him .just been looking through an old avon catalog and for a 10 foot long flat bottom no keel boat with a transom it will give approx 14 mph with a 6hp engine and 1 person and 12 mph with 2 persons,then with 10 hp 18 mph with one up and 16 mph with 2 persons they are only approx and its a very old book but might give you some idea.
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Old 20 March 2009, 09:22   #7
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I had a Bombard AX3 (slatted floor) that with 3.5hp would plane with 1up - BUT dod not like any sort of chop at all . If you want to stay on the plane you may 'need' the slight V hull of the keel, but if you will use mainly on flat ( & I mean realy flat ) water you can get away with the flat floor.

I now have an air deck AX2 as tender that wont plane with 2.5 hp........ shame !
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Old 20 March 2009, 14:06   #8
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our club sec in his flat bottomed sib with a 4 hp engine , it will plane one person as long as the weight is well forwards.
I used to have one of those a zodiac SERIE 134 (3.4m long). Ours had a wooden floor and inflatable keel. Ours planed with about 15 stone of load in. We had a yamaha 6hp 2 stroke. We kneeboarded behind it, but only with 1 person in the boat (tut tut)....and it used to take a while to get on the plane with a boarder happy days
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Old 21 March 2009, 10:07   #9
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A SIB with an inflatable keel will be easier to control than one with a flat bottom. It will also be more comfortable in a chop. There is a reason for the keel after all.

Keith Hart
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Old 23 March 2009, 03:41   #10
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I had an avon redstart with a 4hp yamaha, that would skim the surface really well, once had 12 knots out of it when i was about 14!!
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Old 23 March 2009, 06:55   #11
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I had an avon redstart with a 4hp yamaha, that would skim the surface really well, once had 12 knots out of it when i was about 14!!
did you ever try it with the engine on and no floorboards in ...very intresting results lol ,,talk about folding boats ,
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Old 23 March 2009, 07:03   #12
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no i always had the wooden floorboards in, i dont think it would have been very erm.. safe?!
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Old 05 July 2011, 06:15   #13
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Searching in old posts to try to find what boat to choose. There's not many options if you want to do a bargain in Sweden. I decided on the Zodiac 340 cadet fastroller, but it slipped out of my hands and I cannot find another one. I'm also investigating importing a Bombard 380 from finland, but that's no picnic either, and certainly not a bargain.

However, it seems like Peter M and some more has much experience with small SIBs, and I got really interested in this thread. What boats except the 380 has more of a keel to handle choppy sea? I'm going slightly into the ocean so I'd like it to handle there too.
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Old 06 July 2011, 14:11   #14
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We've got a Zodiac 2.85m SIB with a solid floor and inflatable V-keel.

It planes easily with two of us on board, achieving 14-15mph on the GPS. The engine is a 6hp Mariner 4-stroke.

With just me on board the top speed is about the same but it gets there faster. It handles fairly choppy water OK but you need to sit in the boat (as on this picture) as it bounces around a bit.
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Old 06 July 2011, 14:47   #15
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I got a 2.5 mtr bobbard Ax with flat bottom air floor planes great with a 4 hp on I am only 12 stone and have to get right to front thou lol
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Old 21 July 2011, 19:11   #16
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I have a zodiac zoom 3.4 with a 9.9 hp 4 stroke yamaha it has the plywood floor sections with a small inflatable keel under them (the keel has a leak that prevents it staying inflated for more then about 1minute . So it is basically a flat btm) and I can get 2 adult men with fishing gear on plane pretty quickly if the weight is distributed properly ( fuel tank and one passenger up front gear in the middle and driver at back . My top speed on flat water with that set up is about 28 kph

Hope that helps
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Old 02 March 2021, 04:04   #17
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Old thread, but I found it, so others looking may too. I have a 3M SIB, and an old 6hp Johnson 2 stroke will take her to 18mph no sweat 1up. 2 up (200lbs each), she'll plane occasionally, but any disturbance in the water and forget it. Purchased a 15hp Johnson to solve that problem, and separated the tubes from the transom brackets. 10hp is probably perfect. Haven't had flat enough water for to actually speed-test the 15hp, but did see 22mph before dropping my phone to bring the boat back under control. I'd wager she has 25mph in her or more on flat water with the flat bottom, but as soon as you get in the ocean forget about it. Even if your boat and body can take the punishment, you're liable to be bounced out of the boat at any planing speed. As will anything else that's not tied down, while your tank bounces violently and your engine threatens to rip the transom clean off the boat. It's not a wave runner.

Question, can an inflatable keel be "added" between the bottom and an air-floor? And does anyone think that would tame her any, at the slowest of planing speeds (probably 12mph, and probably with the 6hp most of the time on big water, as I don't know what I could use the extra hp for anyway.)
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