porpoising is a sign that the fore/aft balance of the boat is wrong.

is it still apparent when you are light on fuel? my guess is that moving the tanks that far forward probably wasnt a great idea.

a good boat design will have as much of the weight centered as possible, same as cars, bikes, etc.

It still was porpoising when fuel tank aft.. The amount of porpoising isnt bad by any means ,just annoying ( flat water going at speed ) Trimming the motor does help a little but that impedes overall performance ..

mowerman wrote: Do hydrofoils work? ,no doubt this subject has been raised before . The boat is a 620 aly hardtop with a honda 115/4 stroke.In at my local boat shop who suggested they are worth while fitting..The boat is well balanced ( 90 litres ) fuel under front bunks ,In the past they were in the stern of the boat but it made  stern heavy with the honda motor being fairly weighty. No issues with hole shot but a little porpoising  at higher speed with dosnt seem to trim out. The motor appears to be set correctly in its depth Whats the thoughts on fitting one..good move ,bad move and waist of time and money ? ..just dont want to drill holes if nothings achieved ..One thought I had is it would be a hell of a job freeing any line that gets wrapped around the prop

Porpoising is caused by bad hull shape and nothing else, i see a lot of alloy hulls that have poor hull designs or hulls that have warped out of shape.  fitting a hydrofoil can help with the hull issue, but will never cure it totally

had then on all my boats made massive difference on my glass boats but didn't do **** to the surtees

Had Permatrims on most of my boats, made a huge difference to take off without wheelstanding so to speak and could plane at slower revs, much better ride in a following sea going up and over and down the swells without continuously working the throttle.

yep get yourself a permatrim, means bolting it on but then no-ones about to flog it in a hurry...
they make different sizes and colours for different boats and outboards..
if your getting knocked around in a head on sea you can push the sea open as well but just make sure your hull is strong enough to take the weight it can apply to your hull if used this way...
but like others have said it gets you outa the hole reel smart and stabilizes your boat when trimmed right in a running sea...




 

Have just has a permatrim fitted to my rig and has made the world of difference,, Set up is a Extreme Game King 650 with a 200hp 4 stroke Suzuki on the back. The main issues I had were despite adding weight ( via some lead bricks) to the anchor well and putting on larger trim tabs the boat never really like going at trolling speed of 7 knots without having its ass right down in the water and had a tendency to porpoise at speeds between 18-25 knots unless fully trimmed and tabs down. ( interestingly the porpoising issue used to settle down when over 28 knots) The permatrim has completely sorted these issues out as well as making the hole shot almost instant and can now hold the plane at 16-17 knots heading into sloppy seas or a steep sharp 15-20 knot westerly chop without the pounding it used to have in these situations.Wish I had done it earlier.

remember all foils increase drag if they provide lift, basic hydrodynamics.

Tipper wrote: remember all foils increase drag if they provide lift, basic hydrodynamics. Your fuel bill will go up for the same boat speed.   Aeroplanes with fatter wings take off sooner, and land at slower airspeeds, but overall speed and efficiency is compromised.

 

I put a se 300 on my f115. For some reason it would make my 6m HT lay over, almost as if the hydrofoil was working as a wing. It certainly would get the boat on plane quicker and kept it there longer, Fuel wise I didn't think it was any better quiet possibly from the drag the hydrofoil caused. I have taken it of the boat now and any laying over issues have gone.