one very inexperienced boater

[brianhughes]

i have put a 60hp yamaha on the back of a 18' mayland fishing boat goes fine upto and around 30mph then it starts porpoising even on a flat sea, has it reached its max or is there something i can do to stabilize it so i can use the extra power that it still has.

all advise will be appreciated

 

[BarryH]

Theres a lot that can influence the way a hull performs. Engine trim, weight distribution even the wind, my boat leans into the wind when flat out!
I'd say that your 30 odd mph is nearing the top end for your particular hull. If the engine has power trim try trimming in the engine a tad so the hull "grips" the water a bit more. You could try adding a set of hydrofoils to the engine to see if that stops it. Worked on a fletcher I had.

Somewhere on the boat will be a makers plate which should have the recommended max hp for the boat. Make sure your not over the limit as I not totaly sure what engine hp the Mayland 18 can take.

Lots to think about. Try the cheap options first just by playing with the trim of the engine and moving stuff forward to spread the weight. Good luck with it.

 

[ballena]

What type of hull does the mayland 18 have? from memory I have a feeling its a semi-displacement job although I might be wrong.

Can you trim the engine in to push the nose down a tad? or move some weight forward.

Either way it sounds like you might be pushing it with that engine.

 

[capnjack]

There's a Mayland 18 advertised at Essex Boatyards with a Tohatsu 120 on the back. From the looks of the hull design I would have said it ought to be a planing hull. The transom vee seems to have about 16-18* off deadrise, take off the superstructure and some of the freeboard and you've got a small sportsboat. Well not quite but you know what I mean.

If you're not very experienced with boats, trimming them can be a tad hard. I think the other two posts have already offered very good, sound advice. I'll add two penn'th as well though.

Is the engine flat out at 30, that is 5,250 - 5,500rpms? What does the prop look like, is it clean or scarred, paint chipped etc. How old is the set up? Have you tried a little weight distribution to see if anything happens to the porpoising?

Do you have any more specific information available?

 

[tcm]

hm. 30mph sounds quick anyway altho not very boaty (it shd be in knots, really). Try geting 3x massive black outboards which all say "250 TTi z injection" onnem and nail them on, and i bet it will go faster. If there is any porpoising it will be more realistic in terms of diving underwater and then leaping high into the air, repeatedly

 

[dralex]

Didn't Jimi design a similar boat last year- I remember a picture?