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Old 15 October 2011, 07:18   #11
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Originally Posted by m chappelow View Post
...another cause is that it may have gone out of shape for some reason ,(hogged)or sat on trailer and been full of rainwaterfor months on end causing the bottom fabric to stretch and to go concave when in the water .
one uk rescue organisation used to put their sibs on a jig each year to see if the hull was out of shape.
BINGO; when I first bought it, I took out all the floorboards for maintenance, leaving the hypalon fabric half inflated on the trailer. It could well be hogged by during that period.
Didn't know the fabric could even be stretched like that. But now you're saying...

Is there a way to test it, and how can it possibly be restored?
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Old 15 October 2011, 12:21   #12
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Has anyone experience with the hogging & bogging phenomenon/ overtstretched hull on SIB's, and can it be fixed?

I am pretty sure that is my problem, considering the slack in the hull when fully inflated..
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Old 15 October 2011, 14:38   #13
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Quote:
Originally Posted by TheMadMariner View Post
Has anyone experience with the hogging & bogging phenomenon/ overtstretched hull on SIB's, and can it be fixed?

I am pretty sure that is my problem, considering the slack in the hull when fully inflated..
Not 100% sure i understand the construction of Your boat. But if the issue is that there is too much "slack" in the bottom fabric, you might try to tighten it? This by adding some material between the fabric and the wooden V pices. If You have a few of those closed cell sleeping pads try to put that stuff between. No idea would it work but at least the fabric would be tighter and a the test is cheap?
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Old 15 October 2011, 16:48   #14
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Years ago, the fabric stretched in our Avon with a wood deck and performance became eratic. While considering a replacement boat, a lady at Achielles, who was familar with that type of problem suggested I replace the front floorboard section with a longer piece to make up for the stretch.

Put in a new floorboard section and the problem was solved. Have no idea how your floorboards fit, but a loose bottom will ruin the ride of a boat. It takes very little stretching of the fabric to cause the floorboards to require attention.
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Old 15 October 2011, 17:57   #15
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Thank you lads for all input!

In the last 24 hours, I've received more and better tips from you guys then I did in all phone call's to both prof workshop's and dealer's. That's why I love this forum.

@ frankcc, that's definatly worth trying, because when I take out the front thrustboard and decide to go for a ride, the boat is porposing just as bad as he would with the front board installed.
Save to say the current thrustboard isn't helping in stretching the boat.
But how did you figure out how much length you needed to make up for the stretched hull?

Thanks,
Chris
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Old 15 October 2011, 17:59   #16
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So, the motor height (cav plate even with transom bottom) and changes in trim had no change? In your last video I looks like the trim needs to be a little more out, away from the transom to lift the bow a little. Unfortunately for us sib owners, it is necessary to change our trim very often as out load changes. Also, as stated earlier, if you don't have a gauge, get one as tube and keel pressure can change performance dramatically.

(I also have a bombard C3 like Captnjack, but have no performance issues. It has a tohatsu 40hp (maximum rating) and the thing screams! I haven't personally clocked it, but the guy I got it from swore he and his friend clocked it at 40 mph with a gps!)
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Old 15 October 2011, 19:04   #17
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@sinner,
I wish it did made a difference, but I have mounted the motor small bits higher and tested everytime, up to 1 inch above center-line keel. Changing between the trim setting with every correction. It all didn't made the difference I hoped for, and did not stop the porpoising. Also the weight distribution; been there done that, to no avail. You can repress the purpoising, but that simply worsen the performance.
Hope to reach similar performance of your set-up, I believe the topspeed of mine could well be ~32 mph with the right prop.

Next stop is the forward thrustboard, will keep you guys up to date on that....
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Old 15 October 2011, 21:42   #18
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MM, built a mock up from hardboard too long on purpose. Used the front shape of the old floor section to capture the correct curves. Then by trial and error cut the length of the hardboard until it appeared to fit too tight. Then used the hardboard as a pattern to cut the marine plywood which was then trial fitted and shortened as necessary to insure the boat bottom was stretched tight.

The handling improved to what it was when the boat was new. We still have the boat and many years from making the floorboard, the performance has not changed. I may be wrong, but after the stretching of the bottom initially, it does not have the capacity to stretch much now.

I would recommend something like this for your craft, as a loose bottom is the pits.
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Old 15 October 2011, 23:04   #19
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....

I would recommend something like this for your craft, as a loose bottom is the pits.
No one likes a loose bottom!
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Old 16 October 2011, 14:48   #20
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Results incoming!

Today I achieved to extend the floor the lazy man's way; by jamming an 1 inch thick piece of wood between the two forward floorboards. (see 1st picture below)

After inflating the thing, the hull sure did seems more rigid then before.
I decided to go for a testride.

And, to my genuine surprise; the boat planed and didn't porpoise! Throttle up to an incredible estimated ~ 25 mph, @ 3500 RPM, before it start to bounce once again, but less violent then it would otherwise.

As you can imagine, I am one happy bloke now
It might be some work to achieve the exact lenght to make up for the stretch, but we're finally on to something.
I might mount the motor higher up a bit as well, to add performance. (see 2nd picture)
Any thoughts on that?
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