Getting onto the plane 2

[Captain Coochie]

So i dont hijack the other thread .
Ive only taken the runabout out with a 25hp on it once and tried to get on the plane . I was told a 25hp merc outboard would be more than enough for this but the boat didnt flatten out . A friend i had with me said i needed to weigh down the bow and suggested he go and sit on the bow ( much to my ammusement ) He saw my grin and thought better of it
Anyhow my question is , do i need to weigh down the bow and is there some formula to work out how ballast is needed or is it trial and error ?

 

[MapisM]

Anyhow my question is , do i need to weigh down the bow

No. In principle, with a planing boat you always want to keep weight as low as possible.
In fact, depending on conditions, it might be useful to increase the stern lift or the bow lift.
But "lift" is the name of the game, never "weigh down".
If as I suppose you don't have any load astern which you can get rid off, trim tabs is what you need to increase the stern lift while getting onto the plane.

That said, it's true that - AOTBE - if you can shift some weight forward while getting onto plane (as your friend suggested) you can get a similar effect, but putting ballast in the bow is just a patch, not a proper solution.

 

[Greg2]

Without wishing to contradict MapisM it can help to shift weight to the bow on a tender/runabout just to get on the plane. MapisM is right in principle that lift is the name of the game but I have had tenders which, particularly when fully laden, have taken a shift in weight (a person) forward to help get over the hump. Once on the plane the weight can be shifted back and the boat will usually stay on then plane.

 

[MapisM]

No contradiction at all, I also said that shifting weight can help.
It's adding some fixed ballast what I definitely would not recommend.

PS: if you think about it, shifting weight towards the bow is actually a way to lighten the stern, hence improving the stern lift, which is what we're aiming at really, rather than "weighing down" the bow.

 

[Captain Coochie]

Hmmm i dont really want to be adding trim tabs to the boat and shifting weight is also a bit of a problem as the boat is 6ft to the wheel and 7ft of foredeck that you need to go head first into and twist your legs in and then try and get out backwards .

 

[MapisM]

I see... You mean that she's 13' LOA, or am I misunderstanding something?
Because the smaller the boat, the less I would want to ballast her.
Maybe you could consider the Smart Tabs which are being discussed in this other thread.
They aren't expensive, simple to install, and I bet that on such small boat they would do a good job.

 

[Wavey]

Dad used to race a Tremlett aptly named "Lady Turtle" in Class 3 back in the seventies and the only way of getting that on the plane was to lie on the foredeck on his stomach. Once it got going it was simply a matter of sliding backwards and dropping into the seat.

 

[Davy_S]

I run a 15ft boat with a Honda 25hp. When I bought the boat i knew the fat git owner had problems planing. Tiller steered, heavy Honda etc.
What I did was to raise the engine by 2 inches, it was to low in the water.
I moved the 25 litre fuel tank into the forward locker, also placed my spare fuel drum 15 litres, into my anchor locker. Then I put an Atwood hydrofoil fin on the motor. The results were as expected, straight up onto the plane and a top speed(GPS) of 21 knots, plus no dropping off the plane at cruising speed around 12 to 15 knots, Very pleased with the result, previous owner slightly pi££ed off!

 

[Captain Coochie]

No , no misunderstanding . She is 13ft but most of her is foredeck .

 

[MapisM]

Niiiice!
I would still stand my previous suggestion, fwiw.
Together with "shifting" whatever load can be moved, as per the last suggestions.
But I'd steer clear of fixed ballast.
All the best for your tests, anyway!

 

[Captain Coochie]

Im a bit confused as the boat hasnt had trim tabs before but is clearly made to plane . How did they do it before ? Lighter outboard ? There is no weight to shift as there is me by the wheel and an outboard . As more than 50% of the boat is bow thats putting all the weight to the stern .
I noticed on the other thread props are mentioned . Maybe thats the solution ? I really dont want to get into fitting modern items to her as that would also involve adding a battery and other bits and bobs when she is just a day boat to have a bit of fun on .

 

[grumpy_o_g]

No , no misunderstanding . She is 13ft but most of her is foredeck .

I think I can see your problem. You're sitting in the wrong place and facing the wrong way. You've been watching to many rowers - you should sitting behind that wheel thing facing forwards. No wonder you MoBo-ers get a bad rep if that's how you drive them....

 

[darren_v8]

The fins that someone mentioned may help, or the smart tabs that I'm looking into. The fins may be better to try first as no one will see them so will not spoil the aesthetic of your boat, the advantage of the tabs over the fins are that they are spread wider apart making the boat more stable. I have the fins on mine currently and she gets up on plain no problem, but she is 14' with a 70hp motor

 

[Captain Coochie]

Fins as in the ones to extend the fins on the outboard ?
The boat is mainly for inland diddling about so i have a smaller outboard for that but i have the 25HP if i want to take her somewhere else . I think anything more than a 25 and she would take off . She is so light if i could actually grab hold of her i think i could pick her up on my own .

 

[sarabande]

err, have you tried adjusting the trim angle of the leg ? It looks a bit far out - which might explain the bows up attitude.


The angle of thrust is very important, but I guess you know that.

 

[MapisM]

Im a bit confused as the boat hasnt had trim tabs before but is clearly made to plane . How did they do it before ? Lighter outboard ?

Possibly. Or maybe a tad more powerful, difficult to tell unless you know some of her history.
Did you try moving the tank as forward as possible, and also stand on leaning forward? It might well be a matter of just shifting a BIT of weight forward.
Re.props, of course a shorter prop would improve the holeshot, AOTBE.
But I would try as much as possible to get her up as she is, to start with.
Maybe, once planing, the existing prop would prove correct.
In which case, trim tabs would definitely be a more appropriate choice than shortening the prop.
Btw, I don't think that those Smart Tabs require any battery power.
I would also second Sarabande suggestion: if the O/B is not trimmable, you might try tucking it in one step.
The fins on the cavitation plate, I just hate them. But that's me.

 

[Captain Coochie]

I have full history for her but she has been in storage most of her life so no actually race history .

 

[dianoce]

Fins as in the ones to extend the fins on the outboard ?
The boat is mainly for inland diddling about so i have a smaller outboard for that but i have the 25HP if i want to take her somewhere else . I think anything more than a 25 and she would take off . She is so light if i could actually grab hold of her i think i could pick her up on my own .

If that is the case, I think I would go with the suggestion of adding weight on the opposite side of it. That would reduce the freeboard aft, but it would also reduce the speed.

 

[darren_v8]

Fins as in the ones to extend the fins on the outboard ?
The boat is mainly for inland diddling about so i have a smaller outboard for that but i have the 25HP if i want to take her somewhere else . I think anything more than a 25 and she would take off . She is so light if i could actually grab hold of her i think i could pick her up on my own .

The fins I'm talking about fit on the outboard just above the prop. You can see them on mine just under where the gearcase turns white, they're black

 

[Captain Coochie]

Yup ive seen them . Re the prop angle . As its an outboard i only had the pin to adjust it but yes i do know about that and there was two of us looking at it . Might be worth playing with that though as when i got her wet it was more to do with any leaks . There wasnt so we went silly to see if the back got ripped off