High X Dim.

[PatriYacht]

I like the idea of adding extension boxes to the boat. Generally you can raise the drives one inch if you add them. The props will be deeper when getting on plane and shallower at high speed. Also they increase trim leverage by putting the props further back behind the hull's pivot point. It's just a lot of money and work. I prfer the Imco boxes because they retain the Merc drive coupler and it's rubber cushion.

 

[Tinkerer]

RIK - What I mean by ventilate the props is what happens when you surface the props to get air in front of the blades to free them up. It is not what I call slipping when getting on plane.
My boat doesn't seem to need a lot of trim to raise the bow but it feels like I am trimming only to free up the props.

CORRECTION - I checked the depth of the drives tonight.
With the drives tucked in the point of the IMCO drive is 4 inches from the bottom of the hull. With the drives set at 3 ( neutral trim ) they are 5 inches down.

 

[Tinkerer]

I too was thinking on putting IMCO boxes on the boat.

If I do the boxes I think I am going to go up about 2 inches. If I don't do boxes I think it will be 1 inch up.

My prop shafts right now are about 1 1/2 inches higher than the bottom of the V.
The bottom of the bullet is even with the bottom of the V.

 

[Tinkerer]

I will take a picture of the drives in relation to the bottom of the boat when trimmed for max speed. I just feel I am wasting a lot of thrust pushing the stern down instead of the boat forward.

 

[Tinkerer]

RIK - Who is Sprague Mullikin - Is he a member here?

RIK - The trim angle is what I think as severe, How do you know if you are trimming for bow lift or just trimming to ventilate the props. I havn't tried to trim till they blow out.

The reason I think that I can raise the drives is that I raised them 2 inches already with the same style props and the trim angle stayed the same for max speed.

 

[DAREDEVIL]

RIK - Who is Sprague Mullikin - Is he a member here?

RIK - The trim angle is what I think as severe, How do you know if you are trimming for bow lift or just trimming to ventilate the props. I havn't tried to trim till they blow out.

The reason I think that I can raise the drives is that I raised them 2 inches already with the same style props and the trim angle stayed the same for max speed.

OK,,here i go again. DON't USE BOXES and leave thedrives where they are.
Yes if u use boxes go up 1 inch to get water to the props.

BUT U NEED TO FIND THE RIGHT PROP NOW AND LEAVE IT !!!!!!!
Just trusst me ?!
Every thing else is a waist of money,,i been there !!!

The max speed on a boat that is dialed in perfect should be when the drive is neutral or maybe +1 not more.
Best forward thrust.

If u need that much trimm u need to add a rocker or find the right props to lift your bow.
I know alot of people will say i am crazy,,but hey,,,all i can say is OK .LOL

 

[Tinkerer]

But wouldn't boxes help with bow lift more than any prop.
The maximus 5 blade props with the higher rake would give me more bow lift wouldn't they?

BTW - the props are turning in

 

[MOBILEMERCMAN]

My prop shafts right now are about 1 1/2 inches higher than the bottom of the V.
The bottom of the bullet is even with the bottom of the V.

Tink,

Generally speaking when you talk about height it is with the prop shaft parallel with the bottom. The height numbers change wildly when the drives are trimmed.

It is beginning to make more sense now. Mid 80's boats drives were usually buried. Down about 7 to 9 inches. You mentioned with drives neutral you were 5 inches down. That makes sense if you have 2" shorties.

So to get to the target height of about 4 but not less than 3 you do need to go up another inch maybe 2. You at 5 down are still relatively deep. Most boats built more recently start at where you are now. Velocities are the first I am aware of that started raising their drives on production boats in late 80's. There are likely others too.

The measurement I previously mentioned relating the prop shaft to the bottom of the V is not a hard fast rule just something to keep in mind. Boats with 24* deadraise can run side by side heights higher than 26* boats as an example. The point is you still want props to be biting as the hull releases.

Make all height measurements with shafts parallel. That is the constant that makes any discussion on heights possible.

 

[DAREDEVIL]

Tink,

Generally speaking when you talk about height it is with the prop shaft parallel with the bottom. The height numbers change wildly when the drives are trimmed.

It is beginning to make more sense now. Mid 80's boats drives were usually buried. Down about 7 to 9 inches. You mentioned with drives neutral you were 5 inches down. That makes sense if you have 2" shorties.

So to get to the target height of about 4 but not less than 3 you do need to go up another inch maybe 2. You at 5 down are still relatively deep. Most boats built more recently start at where you are now. Velocities are the first I am aware of that started raising their drives on production boats in late 80's. There are likely others too.

The measurement I previously mentioned relating the prop shaft to the bottom of the V is not a hard fast rule just something to keep in mind. Boats with 24* deadraise can run side by side heights higher than 26* boats as an example. The point is you still want props to be biting as the hull releases.

Make all height measurements with shafts parallel. That is the constant that makes any discussion on heights possible.

We agree again,,altough i was thinking he knew that,,,,,,,,,,but hell yes, if u are still -5 inches ,then go up but not with boxes.
If u do add boxes (which i would not) then remember to go up an other inch.
Rule of thumb is for each 10 inches back u need to go min.1 inch up.
Thats why i like the stelling boxes if any ,because u can play with the hight and not move the engines.
:USA::seeya:

 

[DAREDEVIL]

But wouldn't boxes help with bow lift more than any prop.
The maximus 5 blade props with the higher rake would give me more bow lift wouldn't they?

BTW - the props are turning in

I had mine turning out on my 33 PP, and actually gained speed.
Some people tell me i am wrong,but maybe u should try that and see if it losens up the hull more.
On a bravo thats easy,just change props and run in reverse. ( ONLY ON BRAVO's )

 

[MOBILEMERCMAN]

I would turn them out too.

 

[DAREDEVIL]

I would turn them out too.

Damn,,,again we agree. Now its getting wiered. HEHE:sifone:

 

[PatriYacht]

RIK - Who is Sprague Mullikin - Is he a member here?

RIK - The trim angle is what I think as severe, How do you know if you are trimming for bow lift or just trimming to ventilate the props. I havn't tried to trim till they blow out.

The reason I think that I can raise the drives is that I raised them 2 inches already with the same style props and the trim angle stayed the same for max speed.

Sprague is aka BenPerfected. He has a 100+mph 30' Scarab and he has played with drive heights a lot on his boat.

 

[Tinkerer]

here is a picture at neutral trim.

 

[Tinkerer]

here is the trim setting for max speed.

 

[Tinkerer]

Yes I know the boat is dirty.
It hasn't been on the water in three years.
And part of that time it was sitting in mud.

The trim looks a little too much.

Did a little checking tonight.
Neutral trim is at 4
Max is 8 or 9

Prop shaft at neutral trim is 4 7/8 down from the closest part of the hull.

Daredevil - why are you so dead set against boxes.

I badly need to add hyd. steering to this boat. If boxes are going to solve my trim problem then I don't want to have to buy the rams twice.

 

[Tinkerer]

It has been a while since I played with the props but I liked the high speed handling better with them turning in.
I don't know if I tested after I installed the shorties.
My wife is usually on the boat and she doesn't like sitting around while I work on the boat.
That and on and off the trailer umpteen times can't be any fun for her either.

 

[MOBILEMERCMAN]

A pic like this with the prop shaft parallel will be more helpful.

 

[Tinkerer]

Do you mean helpfull for you to see the amount of trim - or if my drives looked like yours it would work better..

I can put a staight edge on the hull and have it extend back just below the cav plate so you can see the angle.
But that will have to wait till tomarrow night.

 

[MOBILEMERCMAN]

Trying to see how high they are now. The side view with the straight edge would be helpful too. Straight edge parallel to centerline of boat. Not concerned with trim angle. The parallel propshaft height is what I would like to see.


That is a pic of Amsoil.