Strange problem with SIB hull/ Keel ....?

[sinner]

If you can safely look over the transom while on plane, look to see if the anti-ventilation plate is visible. If should be at the surface of the water. If not, adjust accordingly.

[frankc]

Happy to hear of the improvement in performance. Once you lengthen the floorboard, then you may need to address the inverted v section, but that is a matter for you to play around with.

Adding a Sting Ray or some other fin to the cavitation plate may be helpful as well. They will slow your boat a bit, but if it prevents some porpusing, it would be worth it.

[m chappelow]

Could the wood floor boards have shrunk in size a bit if they have been stored dry a long time and its them thats gone a bit smaller and not the boat thats stretched ,,,any how its easier playing with the floorboards than the boat .

[tommo]

what about adding lifters seemed to cure loads of problems on my 3.5 Honwave?
Easy to make too.

[bingosucks]

you can buy tiller extensions(could be preaching to the converted here) ,which would allow you to redistribute your weight and maybe stop the porpoising at higher speeds

[rocket1]

Thanks to all contributors for their input.
I have had the same problem with my Achilles sgx132 with a merc 30 4s.
I have tried all the trim points such as tube/keel pressure, motor hight and trim, I also have one of those sting ray fins mounted to the cavitation plate and have had it off and on with no change to the porpoising.
Another note is that when this is happening I can actually feel the bottom flexing then it releases causing the boat to pop up then repeats turning into porpoising and the more the boat is loaded the worse it gets.
I have had this idea in the back of my mind for a little while now but am very happy to see you have tested it.
Keep us updated on your progress with the floor mods.

[TheMadMariner]

..somehow 'glad' to hear some else has recognised the same problem as well. Most prof's will tell you to fine-tune things like weight, engine height, cav fin's etc. But with this problem on your hands, those things will only do jack & shit.

Now; to further adress to the problem of a 'overstretched hull'

My progress so far;
I proceeded with lengtening the 'thrustboard', by adding more pieces of wood, adjusting them to fit the rest of the floor. To counter these adjusments, I also had to alter the shape of the forward-thrustboard, (small one,which lies in front of the big thrustboard)
For most inflatables, I think this might very well do the trick.

However, due to both the (awkward) design of this vessel and the intensity of the stretched hull, adjusting the floor alone won't do the job.

To make up for the stretch I tested and finally glued some length of rubber (the black stuff) to the hypalon floor in the exact center of the floor near the transom.

The other place I glued some, is the section just in front of the 'point where the V-shaped floorboards meet'. (see my previous postings&photo to explain) Fully inflated, the floor-tube will push the hull down on this point, avoiding getting myself a stepped-hull-the-wrong-way.
Flipping the boat and looking at the hull, tells me I might have succeeded at this point.

Getting the boat appart everytime to alter the floor is certainly wreaking havoc on one's spare time, so the afore mentioned improvements are yet to be tested....

Next up; mounting some 60 angry horses on the transom and see how it works... will post the results, hopefully next weekend.

Grts,
Chris