Tow/Ski Tubes

Forbsey - We use a circular piece of 10mm marine ply, about 1.2M in diameter, for slow speed fun.
You just need to keep the attack angle right by weight shift, to keep it moving. You can slalom right and left on it, with weight shift.
It's good for about 12 kts. Over 12kts, the friction of the water on the underside will overcome the tow rope pull, and you go off, over the front.
It's good cheap, simple fun. I pull a spectators pleasure stunt by taking an old wooden chair with me, on a deep water start.
You get up on the plane, carrying the chair in one hand, and hanging onto the rope with your other hand - then you slip the chair in behind you, and sit on it, and make like a king being towed on his throne!
Good fun until 13 kts comes up, and you go off over the front. You need to do this in water that's not too deep, so you can recover the chair!

Cheers - Ron.

We sometimes use a round tube hehind a 25hp and with one person it geta up on the plane ok.

From my recent experience it is the weight of hthe person in the tube.
I investigated various tubes and the triangle ones supposed to plane easier than the round.
I found no problem when you have your observer being light also as additional weight in the boat slows in down also.
Mine is a 18HP in a 3.85 tinny

Honky

15 hp is not a lot of HP so will need a bit more detail to help,type of craft, weight of both persons in craft & in/on tube as a rule the bigger the tube the easier to tow (1ltr of air volume will support 1 kg less the weight of container)

As a water skier for the past 20 years , it all comes down to Horse power of your motor - there is considerable load on boat/ motor and tube when first getting going - - what your trying to achieve is less friction/ surface area in a very short time with that said - 20 hp min for a small tinny - understanding that when your towing something out of the deep its the equivalent of driving a manual car and trying to do a hill start in 3rd gear whilst towing a trailer

when moving to the next step - water ski - you then need to jump to at least 100 HP egg beater or 327 chev

i currently ski beind either 350 worked chev - or race boat with 454 with high rise manifold and twin 650 holley carbs - this would pull your tube no probs :)