Bracket build

[Bushwacker]

Originally Posted by strick

. . . 30 inch set back is a bit too much for a 20' foot boat in my mind. The 30 inch set back is for big V 8 motors that go on a 23 foot boat. Another thing....make your flotation chamber as big as possible.

I agree with Strick. The 20' hull is a LOT smaller and lighter than the 23, so the CG will shift aft a lot more with a bracket on a 20 than it will on a 23. In other words, the 20 is a lot more sensitive to both setback and engine weight, so it's best to minimize both, AND make the flotation tank as big as possible! I'd bring the bottom of the flotation tub straight back from the transom like the Hermco and Strick brackets. I wouldn't worry about it dragging in the water coming on plane because I think it acts like a big trim tab and provides some extra stern lift (and drag) in that short transient situation. It looks to me like Armstrong put a taper on the bottom of their bracket to avoid the drag, but they're giving up some dynamic lift and a lot of static flotation with it. I think trading a little extra drag during a few seconds climbing on plane for more dynamic lift and static flotation is a move in the right direction!

[6buoys]

strick i seen yuo used foam in your bracket . first what kind and second is there an advantage over ply other than weight

[FishStretcher]

For a 20 foot seacraft-

Without having made one, but having modeled one in CAD, a 20" shaft inline 4 cylinder 4 stroke gets tight on a 24" transom if you want to tilt it the last few degrees, at least when I modeled a 4 cylinder yamaha tilted up at 70 degrees. At 60-65 degrees tilt, it looks ok.

I think the e-tec powerheads are shorter and you might be able to go to a 22" setback on a 20" shaft motor, maybe.

And I think a 25" shaft motor probably gets the powerhead above the rub rail on the transom on non-master anglers (which have that tall cap).

The pic below is of a 20 foot master angler with a 20" shaft yamaha 4 cylinder 4 stroke (F100)- probably the worst case for clearance, and it still will work at just 24" setback at just a bit less than full tilt up.

Originally Posted by strick

Everything centers around two measurements:

1. Engine shaft length

2. motor clearance when tilted up.

Figure these two things out and the rest comes into place. It is better if you do this in your head and draw it out on paper. 30 inch set back is a bit too much for a 20' foot boat in my mind. The 30 inch set back is for big V 8 motors that go on a 23 foot boat. Another thing....make your flotation chamber as big as possible. Good luck!


strick

[Bushwacker]

Fish,

Here's some more dimensional info for your studies. In the first picture http://i188.photobucket.com/albums/z...tclrncmeas.jpg, you can see that the 25" V-6 E-Tec on my 30" bracket has about 7.5" of horizontal clearance with the filled in transom, to which I have added a rub rail that sticks out about 3/4". I could therefore get by with a min setback of 22.5"; these motors have an adjustable tilt limit switch, so you could go with an even shorter setback if you used that. A V-4 115/130 hp E-Tec would need even less setback, maybe 18-20". When mounted on a bracket, those motors will push a 20' hull to at least 40 mph, and they're about 30 lbs lighter than the V-6, so if you're not a speed demon they'd be an excellent choice for a bracketed 20. The V-6 is overkill unless you run with extremely heavy loads.

Here's a side view of my rig with motor at full tilt on the 30" Hermco bracket. http://i188.photobucket.com/albums/z.../Fltltsdvw.jpg As you can see in this picture, much of the powerhead is actually above the transom, so the horizontal dimension to top of powerhead I quoted above is actually quite conservative. If I had a shorter bracket, the top of transom or rub rail would actually contact the motor about where the decal is on front of cover. I have since raised the motor another inch from when these pictures were taken, so I now have even more clearance than shown. If you'd like more exact dimensions at the current mounting height, let me know and I'll go take some more measurements.
Denny

[FishStretcher]

Bushwacker-

Thanks for the measurements!

I am assuming my pivot point is correct for the Yamaha. It is sitting under 2 tarps waiting for snow...

I plan on on recreating the cap contour atop the transom, so that's what is shown in the model I have. Now I have to find the Yamaha manual and make sure I didn't goof the pivot point. I was lazy and pivoted it about the top of the bracket edge, but it is probably 1 to 1.5" above and forward of that point. With the 20" shaft, I will need the motor low on the bracket, I think. If I could only find a 25" Yamaha F100, it you be easier.

I do have a CAD model of the 130 from the internet. It seems to be the real deal. Maybe I can drop it in and compare. But no E-Tec for me. My F100 was $1000, and that's my kind of budget. Unless I find a 115 Etec for $1000

[bly]

and big the engine cowing is. Between that and the rake in the sea craft transom? I do not see how to cut the bracket down very much. If he wants to be able to tilt the lower unit out of the water.

[todosier]

Originally Posted by FishStretcher

Bushwacker-

Thanks for the measurements!

I am assuming my pivot point is correct for the Yamaha. It is sitting under 2 tarps waiting for snow...

I plan on on recreating the cap contour atop the transom, so that's what is shown in the model I have. Now I have to find the Yamaha manual and make sure I didn't goof the pivot point. I was lazy and pivoted it about the top of the bracket edge, but it is probably 1 to 1.5" above and forward of that point. With the 20" shaft, I will need the motor low on the bracket, I think. If I could only find a 25" Yamaha F100, it you be easier.

I do have a CAD model of the 130 from the internet. It seems to be the real deal. Maybe I can drop it in and compare. But no E-Tec for me. My F100 was $1000, and that's my kind of budget. Unless I find a 115 Etec for $1000

I'm doing a similar thing and have the same interest in clearance. I have a pdf of the yamaha rigging clearances for all their outboards, that has every clearance stat you could want. Let me know if you want it.

T

[strick]

Originally Posted by 6buoys

strick i seen yuo used foam in your bracket . first what kind and second is there an advantage over ply other than weight

I used corecell. The no rot thing with the foam is the biggest advantage I guess. Corecell has good compression strength but not as good as plywood. The set back on the yellow bracket is 22.5" and if I remember right I built it I could be able to put a Suzuki 140 on it and be able to tilt it up all the way once the Yamaha dies.

strick