outboard bracket force 125

[fisheymikey]

well i have been spending many hours looking for some correct info but cant seem to get a real responce or plans.

i have a buddy that is a master welder and also has to his disposal many different enginers to assist with the build.

My question is for the 125 1988 weighs about 300pounds. i measured the engine is at 12 degree angle.and want it about 16-18 inch back.

does anyone have done or has some schematics for thinkness or what kind of materials i should use

boat is a 18.5 cc trophy 1988

any help would be great

thanks

 

[jerryjerry05]

Not positive???? I'm sure others will comment.
By adding the bracket, I think that will make the standard motor 5 inches too short.

Try this link.
http://forums.iboats.com/forum/boat-repair-and-restoration/boat-restoration-building-and-hull-repair

 

[Frank Acampora]

If you are welding up a bracket similar to the one in the photo, sides should be at least 1/4 inch hard (aircraft) aluminum. DO NOT use diamond plate as it is softer and weaker. The back to which the engine bolts. should be at least two pieces of 1/2 inch aluminum , say 1/2 X 3 or 4 X width of bracket spaced to match the upper and lower mounting holes in the transom clamps.. The front where it bolts to the transom should be the same with a plate of 3/16 to 1/4 inch covering and welded to the sides. . ALL welds need to be full penetration. AND, it wouldn't hurt to weld in some corner gussets as vibration will tend to want to crack there.

Remember that aluminum is expensive and unless you have a source you are probably going to spend in excess of 200 bucks in materials.

While I have not actually made a bracket (because I didn't need one) I have done a number of transoms with no problems using up to a 150. For my transom replacements I use .080 aluminum, braced and cross bolted together. If you want to see a small one, youtube Frank Acampora videos--mini racer, Chrysler 60.

Understand the a 16 inch setback like you desire will change the handling of the hull. You will DEFINITELY need to raise the engine, maybe as much a 5-6 inches so allow for that when mounting the bracket--provide adjustment slots. Also understand that with that much set-back there should be a bow lifting moment. You may need to change to a stern-lifting prop.

However, if done properly and set up correctly I suspect that hull should be able to achieve well over 50. If you look for help at the prop forum, you will very likely get the question " Why bother with a Force?" Ignore any naysayers.

 

[Frank Acampora]

The reason for lifting the engine with a setback: Planing hulls do not plane flat on top of the water. They assume a shallow angle, carving a "trough" into the water. As the transom passes a given spot, the displaced water rushes back in to fill the trough.The further from the transom the engine is, the deeper it will sit in this replaced water--up to the point where it would be at the depth that the hull displace water. The anti ventilation plate will be buried in as much as six inches of water.THUS: The further back the engine is mounted from the transom, the higher it must be mounted to assure that the anti-ventilation plate is at the correct height.

 

[fisheymikey]

well frank thats what i really needed.. some details.. but now im not too happy with the raising the engine part. i do have an other bottom leg.

i currently have the 25 in shaft i could change it to the 20. and still keep the angle and height. is that correct?

but after your amazing read im guessing scratching the whole project. but still would like to know about changing to another leg

thanks frank

 

[Frank Acampora]

There is a problem with changing the leg: Even after you make the bracket, you simply don't know how far you need to raise the engine. It is experimental. It could be as little as 2 inches or as much as 6 inches. all this varies with the hull design. NOW: If you can find someone who has done something similar to an 18 foot trophy, then you have a solid starting point.

When doing something like this, because you have no other people's experience to guide you, you simply can not expect everything to be just right the first time. For example:

When I modified the transom on my 10 foot mini Cougar Cub, I spent about 3 seasons experimenting. The engine was a 20 inch long shaft and the boat was designed for a 15 inch standard shaft. SO, first I raised the transom about 3 inches (because the boat was a tunnel hull and I didn't know where the anti-ventilation plate should be--I took a guess based on a 15 inch leg and was wrong) and in a couple of steps raised the engine 1 then 2 inches. Finally I rebuilt the transom to a full 5 inch rise and raise the engine1 then 2 inches. At that height, I do get best performance but it is very difficult to get the prop to lock-up. Now I am still experimenting with props.

 

[fisheymikey]

what does that mean a propeller lock up?

 

[jerryjerry05]

The difference in the 20 and 25 is the shaft.
To make a change the shafts will need to be taken out and the unit will need to be tested for proper height etc.
The Motor leg is where the change is.It's actually 5 in longer.
If your motor is a 25 now you can't just put a 20 in on and go.
The mid section will need to be replaced.

 

[Frank Acampora]

Mikey: The prop "Locking-up" will not happen with a normal sport hull. It is normally locked up with the water. It simply means that the prop is not ventilating or cavitating, but moving through the water as it should.

When you first gun the engine on a high performance hull. the prop will slip. ventilate, cavitate, or any combination of all three. The engine revs but the hull does not go as fast as the RPM would indicate. At some point as boat speed increases and planning achieves its normal attitude, this phenomenon will stop . The boat will lurch just like sloppily changed gear in a car and the prop will now "bite" the water as it should. That is when it has locked-up

 

[fisheymikey]

thanks frank for the detailed info

really apreciate

 

[fisheymikey]

i really want to put a pod behind the boat without really needing to adjust anything..

Frank if i go to 10-12'' will i stil encounter the same problem of lifting. the main reason why i want to put the pod is the steering cables and throtle cables are in the way. also a major reason is my lowrance structure scan transducer is too long and is not receiving on the side of the engine due to interference.

can it be done?

thanks

 

[Frank Acampora]

You can not change the laws of physics! ANY set back usually requires a degree of raising the engine. Remember that when you set back the engine off the transom you will most likely need a longer steering cable and longer control cables.

ANYTHING can be done if you throw cubic money at it.

 

[fisheymikey]

ANYTHING can be done if you throw cubic money at it.

lol

ok i tried to bend it not break it..