Bracket tub shape opinions

[warthog5]

This poses some interesting point's as the tub on a Seamark is different.

Here is the file from D&D that I used. Don has now put it on his website, so I will show it. I kept this file offline in the past.

http://www.dadmarine.com/doc.htm

He told me after I mounted my bracket that the bottom should be 3in up from the keel.

But that doesn't jive with the rest of the install imfo.

On my boat [different from your SeaCraft's] My motor's are raised to use the bottom motor mount hole [or will be] they are in the next to the bottom hole right now and the anti cavitation plate is still below the water surface by aprox 3/4in when on plane.

The tub size is lacking for 2- DF-140's and I'm thinking of building a bracket now.

http://www.classicmako.com/projects/xshark/bw19.htm

[1bayouboy]

I really appreciate the discussion guys.....

The pics of the seamark look like the tub's bottom is straight back from the transom, parallel with the boat's keel. Not sure the distance up from the bottom. The outline I have is 3 1/2 inches up from the bottom on the center 21 degree deadrise panels, but only 1 1/2 inches above the middle 13 degree panels. I can vary it in any way, but I wanted the max flotation I could fit. I thought the effect should be similar to a stepped bottom.....but what do I know....it's my first attempt.

I could run the 21 degree deadrise portion farther up before the transition to 13 degrees. I avoid trying to slope the tubs bottom upwards as it goes back just because that seems harder to lay out in a way to build a mold.

[1bayouboy]

Looking at the D&D page, it looks like the top of the bracket where the motors mount is supposed to be 28 1/2 inches above the boats bottom in line with the motors. That's moving the motors up 3 - 3 1/2 inches....but I thinki t assumes the anticavitation plates will be below the bottom of the bracket.

[warthog5]

The pics of the seamark look like the tub's bottom is straight back from the transom, parallel with the boat's keel.

That is correct from what I see too, thus it has more flotation.

The flotation can be deceiving for us average Joe. it's not until this stuff is all mounted and floated until you get a better understanding.

Let's look at the side of the tub alone. Where will the waterline be?

Upon first looking at it will it be 3in, 4in or 5in from the underside of the platform?

The point here is, that anything above the waterline just add's weight and has no effect on flotation to help the boat sit level.
Only what is submerged does have a effect. So we want more area that will be submerged to help the boat sit level.

That means a wider and deeper tub. It also means more volume going aft of the transom.

From this:



To this:

[1bayouboy]

And it looks like if that motor was trimmed all the way down, the anticav plate would be just about at the keel of the bracket....

Nice that the bracket has a prop pocket for the trolling motor...

[SCSeacraft]

Give me a shout if you need another set of hands,as long as one of them has a cold one in it of course!

Here are some pics of your junk from Bobby G's Place, thought you might want them.



You may need to change her name to "Playmate" after the stack of 1978 Playboys that came out of her!

Donnie

[1bayouboy]

You're on there SC.......I think the beer to epoxy ratio is 1/1...

Some quick calc's....with a 28 inch setback and a width of 52 inches that'll be 1456 square inches...or 10.1 square feet. So for every inch above the sloped bottom it sinks in the water, that's 0.84 cubic feet...which is 50lbs of flotation. The V bottom is about 8 inches down from the corner so that should be equivalent to 4 inches for the area
which would be 200lbs of water. So I should have 400-500 lbs of flotation...... The old water line on the transom was about 18 inches up from the keel which would give me 14 inches or so of bracket in the water. I think I need more beer to think about this any more...

[SCSeacraft]

Why don't you just go buy the aluminum bracket I have up at Bobby's place and be done with it??
Donnie