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Old 08 February 2012, 10:30   #11
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Country: USA
Boat name: Black Dragon
Make: Avon Typhoon S4.00
Length: 4m +
Engine: 30hp Johnson
Join Date: Jul 2011
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Thanks but I have the Avon pressure gauge and have tried under, over and proper inflation pressures according the original owners manual.

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Old 08 February 2012, 12:08   #12
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Town: yorkshire
Boat name: little vicky
Make: avon ex RNLI
Length: 3m +
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if you can run the boat about for 5 or 10 mins and then go around with the pump and top up see if that makes any difference starting with the bow working back and the keel last .
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Old 09 February 2012, 03:19   #13
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Originally Posted by russhenchman View Post
Thanks but I have the Avon pressure gauge and have tried under, over and proper inflation pressures according the original owners manual.
1) It's important to get the correct pressure whilst the SIB is IN the water.
2) It's important to get the balance of the boat right (if solo, then a tiller extension may be required to move weight forward etc).
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Old 09 February 2012, 05:47   #14
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Country: UK - Channel Islands
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Make: Arctic 28/FC470
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Sounds to me like you might have too much weight forward, the bow could be getting stuck into the water causing the boat to steer by the bow. I've experienced something similar to what you describe.
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Old 10 February 2012, 14:51   #15
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Country: USA
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Boat name: El Barco Más Rudo
Make: Avon
Length: 4m +
Engine: Tohatsu 40HP
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Originally Posted by martini View Post
Sounds to me like you might have too much weight forward, the bow could be getting stuck into the water causing the boat to steer by the bow. I've experienced something similar to what you describe.
That's the issue with my boat. If there's too much weight near the bow, the boat bucks and the stern rises, causing the prop to aerate. I took the hydrofoil off the outboard to reduce stern lift but it can still be an issue if there isn't enough weight aft.

Another thing to try is adjusting the trim on the motor. Moving the prop closer to the transom keeps the bow down and can increase stability.

Lastly, there's a weird thing I've noticed about my boat is with regard to the surface conditions. When the water is flat calm, the boat will porpoise quite a bit and I have to throttle back. If there's a moderate ripple on the water, I can run at WOT without any problem at all. (Running fast with too much wind chop will knock your fillings out, of course )
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Old 10 February 2012, 16:00   #16
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Dude, sounds like your hull is dragging. That's a weight transfer issue.
Be prepared to shift your weight in the boat as you're changing your boat's state.
From standstill your crew will have to move their weight from the stern to the bow as you build speed to get you planing and then come back a bit once you're there.
It's an organic thing.
But from the off you have to make sure that the standards of your boat are just that.
Let your SIB assume the temp of the water and get it right once the boat has met the water temp, so take the pump with you and fill once you've been on the water for about ten minutes. It's not just the tubes that meet the temp but the air inside them, and generally they will cool and make your boat bendy.
Imagine the weight transfer a motocross rider imparts when on the bike, over the bars when turning, over the rear when under power, hanging off to initiate a turn etc., same with the boat. Especially a sib. The longer the sib the less rigid it is.......tubes may be larger but the material is still the same gauge. And so it is that it will need more input (weight transfer) once underway.
A 5m sib is bendier than a 3m one, but this can be overcome with crew weight transfer.
You are already noticing the reaction of the boat to the conditions. Your crews' reactions need to counter those very conditions.
If it means getting your passengers (crew) onto the bow to get you out of displacement and onto plane the get them to move forward and bring them back a bit to balance your vessel once planing. It's all good fun, involving and effective. Essentially it's an organic process using your feel for what's required by allowing your "mobile" ballast to trim the vessel. Transient ballast is a very expensive commodity in the most expensive of craft and you have it here for free ( unless your mother-in-law refuses to budge).
Main thing is to get everything that's standard, correct. Pressure ( and do it right, on the water), engine (weight,prop,shaft and trim)..........the rest is moveable. Find a medium, fix what you can, tanks etc., and let the crew know that they are part of the boat and not just passengers. You'll feel the difference and so will they.
And if you're singlehanded then get a tiller ext and be prepared to get yourself up to the bow when you're WOT. but be ready to scramble back when you've gone over the top.
Weight transfer. Pressure. Rigid vessel.
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Old 11 February 2012, 17:24   #17
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Country: USA
Boat name: Black Dragon
Make: Avon Typhoon S4.00
Length: 4m +
Engine: 30hp Johnson
Join Date: Jul 2011
Posts: 13
Guys, thank you all for your thoughts...much appreciated.

The boat has no issue getting on plane with the 30hp (2-3 seconds with 3 people).
The bucking will happen with only a gas tank and myself in the stern and nothing up forward, although it is more pronounced with crew on board.

From everyone's input I'm thinking:
1. Ditch the hydrofoil. No need for it.
2. The Avon gauge, although feels heavy duty, is 30 yrs old. Maybe it's not calibrated correctly causing under inflation. This would make the most sense.

I will report back this spring...hopefully with success!
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