OS and Thundertiger style mount systems...

[Kris Flynn]

This question is refering to the OS and Thundertiger style mount systems

Can anyone tell me how much angle you need to put on the pivot pin to actually see an effect regarding cornering and such?

I have put upwards of 1.5mm under the bottom of the transom mount bracket but I cannot see a difference when using a ruler to see if the caveplate is flat when boat is going straight, and when boat goes into turns.

Is there something I am missing??

My twin FE digs the nose a bit in the corners, but flies nicely down the straight...Using 2 REK Lower units and an adapted OS mount.

Cheers

Kris

 

[Tim_Duggan]

Kris,

I like between 1/2 a degree to 1 degree in front of the pin. Definately gives a better cornering attitude on my boat. 1.5mm sounds excessive but I don't use shims so can't say for sure. This for a single though - never tried a twin.

Is the pin exactly vertical? Have you tried twisting the mount slightly? Tried a more rearward CG with some negative behind the pin to keep the attitude in the straights? Tried reprofiling the skegs for less lift?

 

[Kris Flynn]

Hey Tim,

I too thought 1 to .5 Deg helped, but in doing some testing and having my boat on my setup board and changing the angle of the pin, then keeping the angle of the prop shaft at .5deg neg I could't see any change in attitude when the unit was turned from side to side

I havn't played with skeg angles they are bone stock...I do know that my prop shafts are dead parrallell over about 200mm from the drive dog

Cheers

Kris

 

[Jerry Wyss]

The hinge pin to be vertical would have to be at a "right angle" (90*) to the last few inches of the sposon bottoms.

With the pin angled to 91* (top back and zero'd thrust) to the sponsons will give the tendancy to raise the bow when

you turn.

The opposite should happen when you go to 89* (then zero the trust),, the bow should come down when you turn.

I can put 88.5* in my Lynx (then zero the thrust) and scrub half its speed off in the corners. Just that little amount will

pin the sponsons so hard in the corner that it will seem like you hit the breaks while turning, still at full throttle,,,

Bad idea!

 

[Tim_Duggan]

Kris,

You should see a difference in height at full steering lock compared to the steering at the centre position if the pin is not at 90 degrees to the running surfaces. It's not a huge amount if measuring via height at the cav plate - Maybe use a straight edge attached to the transom and measure further away from the pin for more accuracy? I use a digital level to check mine. it will show (in increments of 1/10th of a degree) a variance and does show the propshaft angle decreasing from negative as more rudder is fed in.

However, I'd suggest that trial and error is the best way to find the sweet spot, then measure it as a reference. Don't forget lift @ the stern has an effect on the tendency you are fighting.

 

[Ronald van Essen]

I don't know if the stiffness has something to do with it...the REKlowers are a little more flexible then the metal lower units.

Ronald.

 

[Kris Flynn]

Hey Ronald, how are things?? The REK unit are a little less rigid, but still pretty good I think...Not sure this is the Issue

Jerry, that is exactly what I wanted to hear from someone, which angle (+ or -) does what, because I couldn't see a difference...

Now can you tell me how to cut the skeg to reduce lift? Remeber I have 2 skegs and I think Tim was right in saying the lift in the lower unit is hurting me.

I tried some Stumble blocks but they did NOTHING

Cheers

Kris

 

[Grimracer]

What boat do you have this on Chris?...

Grim

 

[Kris Flynn]

Hey Mike,

It is on a 33" tunnel of my design, basically a scaled up version of the hull I had at the Tunnel Champs in 08.

Not sure if this can be fixed or if i will need to go to other units (which is going to cost a fair amount)

Cheers

Kris

 

[Black & Coke]

This question is refering to the OS and Thundertiger style mount systemsCan anyone tell me how much angle you need to put on the pivot pin to actually see an effect regarding cornering and such?

I have put upwards of 1.5mm under the bottom of the transom mount bracket but I cannot see a difference when using a ruler to see if the caveplate is flat when boat is going straight, and when boat goes into turns.

Is there something I am missing??

My twin FE digs the nose a bit in the corners, but flies nicely down the straight...Using 2 REK Lower units and an adapted OS mount.

Cheers

Kris

Hey Kriss, whats up man? I don't have the answer to this question but i do have a twin O.S boat that runs pretty sweet down the straight and around the bends. Maybe i will loan her to you........LOL

Drop me a line sometime

Terry

p.s. the 2009 Worlds was awesome, you guys need to come back over. The new lake is great

 

[Kris Flynn]

OK some more info:

Boat length 840mm

Width 330mm at widest part

Tunnel depth at rear 20mm

Tunnel width 177mm

Tunnel length 570mm

Tunnel AOA +.6 deg

Drive dogs setback 130mm from back of sponsons

Transom is inset 25mm

Props are 45mm apart

Sponson angle 17deg

Herry Terry, Thought you wernt going?

I really want to get over there again, but we are buying a house this year, might have to try and save some extra coin!

WHEN ARE YOU COMING OVER HERE???????????

Cheers

Kris

 

[camaroboy383]

Hey Ronald, how are things?? The REK unit are a little less rigid, but still pretty good I think...Not sure this is the Issue
Jerry, that is exactly what I wanted to hear from someone, which angle (+ or -) does what, because I couldn't see a difference...

Now can you tell me how to cut the skeg to reduce lift? Remeber I have 2 skegs and I think Tim was right in saying the lift in the lower unit is hurting me.

I tried some Stumble blocks but they did NOTHING

Cheers

Kris

Kris, i think the answer your looking for is in jerry's avitar. Look at the way the skeg on that tt lower is cut back with a way less severe angle to it.knocks a little wieght of the already "BIG BONED" lowers too.lol

Also you do have the stock cast muffler cut off the lowers right?

Jerry's pic is a prime example of the cuts.

Alden

 

[Jerry Wyss]

Hey Ronald, how are things?? The REK unit are a little less rigid, but still pretty good I think...Not sure this is the Issue
Jerry, that is exactly what I wanted to hear from someone, which angle (+ or -) does what, because I couldn't see a difference...

Now can you tell me how to cut the skeg to reduce lift? Remeber I have 2 skegs and I think Tim was right in saying the lift in the lower unit is hurting me.

I tried some Stumble blocks but they did NOTHING

Cheers

Kris

Kris, i think the answer your looking for is in jerry's avitar. Look at the way the skeg on that tt lower is cut back with a way less severe angle to it.knocks a little wieght of the already "BIG BONED" lowers too.lol

Also you do have the stock cast muffler cut off the lowers right?

Jerry's pic is a prime example of the cuts.

Alden

He's using the REK plastic lowers ya cod

 

[camaroboy383]

Lol, lol, mental note,read first post thoroghly...!!!

Kris take all i stated above and toss it out the window..lol