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Old 23 September 2012, 16:26   #11
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If boathull.jpg is the result of planing then I'm not getting that.

Must try harder

Cheers
MOTM
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Old 23 September 2012, 16:51   #12
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Your boat will have a hull displacement speed, which will be about 6mph.

You will get to that speed quickly, and with pretty much any engine on the back, a 2hp would probably do it.
But at 6mph the hull will want to get on to the "plane" and the bow will rise up as it tries to do it. You need extra power to get past this point and then the boat is "planing" and the speed will increase rapidly to 15mph or maybe a bit more.
To be honest if you are getting 17mph out of your SIB with a 6hp on the back that's great performance and I wouldn't worry too much about how it is doing it!
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Old 23 September 2012, 18:08   #13
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Cheers Boatnomad

But without having experienced the effect before it's difficult to know. I'll take your word for it. So just to be clear -is planing bow up looking at the sky or bow down waiting for the boat to plough into the sea?

MOTM
No bow to the sky is the boat trying to "get over the hump" and onto the plane. When it levels off again after that its on the plane. If you move the trim pin out a whole it might help (although as others say 17mph with 6 HP is not bad at all) but it might also mean you are timmed out too far and can't get over the hump. Its trial and error. Much easier if there is someone who knows what they are doing around, or you get some training (but beware most schools will stick you in something twice the size, with a steering wheel, and 10x the power which will bear little resemblance to the handling of what you are using).

Whereabouts are you using it?
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Old 23 September 2012, 18:24   #14
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Thanks Lightning

Yes I think maybe what I'm feeling is the boat planing. If, as you say the bow drops again when it's planing, then that is when I feel like throttling back but actually when I should be getting the big boy pants on and keeping the throttle open.

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no mistaking planing would agree 17mph is plane speed ,i`ve found `pumping` the front helps get over the hump
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Old 24 September 2012, 12:39   #15
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First of all you must have all air chambers including keel inflated to min 3.0 psi, with rib on water top if needed after some minutes water rest, if using a pressure gauge the better, trim angle to have engine perpendicular to sea level once sib is floating, usually 2-3 hole out from transom. Move your weight forward and full wot. Bow should rise and then should come down while sib is near paralell riding on water surface.

If you are a heavy champ sitting on side tube will destabilize the sib a bit, for the test sit on middle deck, once on plane, you can throttle down at a point sib is maintained on plane with much less engine rpm and fuel consumption. When you see the sib is sliding well on water and you're at emotion, you are definitely on plane.

Happy Sibbing
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Old 24 September 2012, 13:23   #16
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Thanks for all the input fellas.

Poly - I did move the pin outy one hole to the 3rd hole and it didn't help so maybe I should put it back into the 1st hole and see what happens. I'm using the boat in Shetland mainly to get out for some fishing.

bingosucks - yes I think maybe what I'm feeling is the boat going over the hump so maybe I should try moving my weight around to see what happens.

locozodiac- it's an airfloor but yes checking my pressure once on the water sounds like a good idea -the water is cold up here.

Cheers all
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Old 24 September 2012, 13:30   #17
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My 3.6 meter yam360s will not do any more that 9 -11 knotts without planing. Then will do around 22 knotts at wot, with a standard prop. yamaha 20hp 400cc twin 2 stroke outboard. A more aggresive prop would make the boat faster, but may not plane when loaded with people.

6hp doing 17mph is great, 100% on plane at that speed. The boat feels like the bow is biting into the water, this is normal with a sib keel.... imho
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Old 24 September 2012, 13:33   #18
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Something I've noticed while out in the SIB..

9 times out of 10 it's a case of open throttle, boat planes within 2 seconds, nice clean planing for as long as needed..

But that 1 time out of 10 the boat will sort of plane and pick up speed but water will spray out from the sides at the very front of the boat. My first thoughts are that this must be linked with what most air deck users may be familiar with, a pocket of air which moves gradually towards the transom, underneath the floor, once this has 'popped' out of the back of the boat there is a slight 'jump' like the boat is again riding onto the plane and the spray from the front stops.

I've put as much air in the deck as the stirrup pump and all of my weight will allow (although there is a slow leak of air) so is this just a classic air deck problem??
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Old 24 September 2012, 14:25   #19
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simsy - if that 'bite' of bow into water is a sib on plane thent that's definitely what I'm getting.

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Old 24 September 2012, 14:54   #20
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