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Old 13 January 2010, 07:06   #11
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Arching its back.

I had a similar problem with an airdeck 311. It was caused by the airdeck not being pumped up enough. A wave would accumulate under the rear half of the boat, causing the deck to bulge up, the the boat would climb over it and get back onto the plane, whereupon the process would start again.....
Don't know if your boat is an airdeck, but if it's a wooden deck, is it being held firmly in place??
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Old 13 January 2010, 11:31   #12
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Also found out with four divers and six scuba tanks onboard, the boat takes awhile to plane.
Yah. Try 6 divers and gear. You'll run out of gas before you get up on plane...

You did OK with 3 divers, and even better with 2. And, you've figured out that the ride is softer in the roiled water of another boats wake, so you're doing pretty well.

jky
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Old 13 January 2010, 15:19   #13
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Yah. Try 6 divers and gear. You'll run out of gas before you get up on plane...
I can not imagine getting 6 divers with gear into my little boat. Obviously you have done it.

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You did OK with 3 divers, and even better with 2. And, you've figured out that the ride is softer in the roiled water of another boats wake, so you're doing pretty well.

jky
I already knew that following a bigger boats wake was smoother. Now if that bigger boat would have just slowed down a mile per hour...our ride would have been smoother.

3 divers actually works great! Planes quick enough and there is plenty of room for gear. Although once everyone is in doubles I might change my opinion.
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Old 14 January 2010, 11:05   #14
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I can not imagine getting 6 divers with gear into my little boat. Obviously you have done it.
7, actually. Not a pretty sight. Top speed with the Honda 40 was about 3 mph (at least I didn't have to worry about the no-wake zone in the harbor.)

We only went around the jetty to the Barge.



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Now if that bigger boat would have just slowed down a mile per hour...our ride would have been smoother.
I couldn't run one mph slower. It was that or about 5 mph slower, and throwing a displacement wake.

Later;

jky
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Old 08 February 2010, 20:29   #15
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same problem; but cavitation leads tyo swamping..

Hey guys I have the same problem I am thinking. this is on a MKVI HD with twin merc 90's. I have to find the boats sweet spot, too much throttle and she starts kicking in water over the transom, not enough and we are just under plane plowing water. I had six tanks+ gear a cooler full of drinks and 4 people, total weight estimate of 1100lbs + the engines are a smidgen over the recommended weight . The pontoons were @ 3.1 the keel& speed tubes @3.4 I am taking her out in the morning to trouble shoot it. any ideas ? ill take some footage and post it when we get in...
-AVI
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Old 15 February 2010, 03:43   #16
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figured out..

after scouring the forums, i believed we had an issue with our motors too deep in the water which begins to create drag and torq down on your tubes. this is what i think may be referred to as arching its back. well we raised the motors and the problem of swamping was solved, it also increased our wot speed significantly.
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Old 16 February 2010, 01:41   #17
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The floor is compressing and quite literally arching. Its a SIBs version of porpoising. I had the same issue on a Bombard soft bottom with AL floor. The now curved hull is getting too much stern lift and pushing air into the prop for an instant. The hull arch dissipates and you return to plane to repeat. There's not much you can do besides shift weight (aft usually) to set the stern down a little more consistently. Check that your engine is trimmed level to slightly bow up. The bow up manual trim setting will pose issues trying to get on a plane tho.

With manual trim on a soft bottom, you are kinda stuck living with the porpoising
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Old 09 March 2010, 03:34   #18
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The floor is compressing and quite literally arching. Its a SIBs version of porpoising. I had the same issue on a Bombard soft bottom with AL floor. The now curved hull is getting too much stern lift and pushing air into the prop for an instant. The hull arch dissipates and you return to plane to repeat. There's not much you can do besides shift weight (aft usually) to set the stern down a little more consistently. Check that your engine is trimmed level to slightly bow up. The bow up manual trim setting will pose issues trying to get on a plane tho.

With manual trim on a soft bottom, you are kinda stuck living with the porpoising
Thanks for the reply. I have manual trim, but my Evinrude does have the ability to stop the boat and set the trim wherever I want. I will try trimming it up just a little next time it decides to act up. Right now I would just like to get back to boat diving. Conditions have been craptastic lately.
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Old 26 July 2013, 17:17   #19
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Peter C, whatever happened with this problem?
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Old 27 July 2013, 02:11   #20
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Proper pressures help A LOT! I bought a gauge and added far more air than I thought I needed. So last weekend four of us where out and it still arched its back a little, but no cavitation and it wasn't bad enough to worry about.

If you are not using a gauge it is time to buy one.
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