DIY jackplate any reason this wouldn't work?

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troyschwab

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pacific northwest washington
Hello all,

this is my first post, I've been trolling this site for a while now and I love everyone's ideas and support they provide during everyone's projects..

well, here is the first of many I plan for my little 12' Duroboat. I got a great deal (i think) on the boat for 500 bucks. the problem is I also got a good deal (again i think) on a long shaft 20hp for 900 bucks. I read the cons of having a long shaft on a short shaft boat and decided to try it out. I now know that its time to raise the motor!!!

anyway, this is how I'm doing it and I'd like any feedback or constructive criticism after all in the end I'd like it done right. I'm ok with doing things a little "ghetto" looking as long as it is functional. I'll attach some pics, let me know what you think.
 

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I guess I posted those in the reverse order. I'll know now for next time...
 

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yes that is the wood stain. I live in Washington state and this will be out in the Puget sound a few times this summer but I plan on storing it indoors while not in use. the metal is all stainless so I'm hoping it will hold up nicely.

with the long shaft on the short transom I was pulling up a little water at full throttle over the transom and into the boat. I also feel like the boat wanted to go much faster. I topped out at 20 MPH I was hoping for a little more than that.

how fast should the boat go with a 20hp on it?
 
This is the second time in as many days that I've seen what appears to be a "reverse transom" on a tin at the site.

There is no reason that would not work, you made one heck of a nice jack plate.

However, you have 20 HP on a 12' boat, it seems pretty wide, but there is a chance it may not be rated for that HP. I'd still keep both though, that's a sweet looking 12', and maybe for a winter project, I'd use a wider/deeper piece of ply and give the transom more support w/ that 20 hanging off the back. At that point, you could, or might as well, convert the boat transom to long shaft. Would appear you'd just need to add a few feet of channel over the new transom.
 
the plate in the boat says max rating is 20 hp. and the transom before was smaller (and rotten) with 4 through bolts. the new one is twice the size and has the original 4 holes and an additional 6 going through the brackets all the way to the inside of the boat.


does anyone have an idea of what speeds I should expect? i topped out right at 20 with a passenger.

I will be doing the inside of this thing pretty soon as well. just need more time to dink with it. I'm sinking a cooler into the center of the floor to double as a seat. I'll make a pad for it or something.
 

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Ictalurus said:
This is the second time in as many days that I've seen what appears to be a "reverse transom" on a tin at the site.

There is no reason that would not work, you made one heck of a nice jack plate.

However, you have 20 HP on a 12' boat, it seems pretty wide, but there is a chance it may not be rated for that HP. I'd still keep both though, that's a sweet looking 12', and maybe for a winter project, I'd use a wider/deeper piece of ply and give the transom more support w/ that 20 hanging off the back. At that point, you could, or might as well, convert the boat transom to long shaft. Would appear you'd just need to add a few feet of channel over the new transom.


If I were to convert the transom, would that require welding the aluminum? I have a mig welder, but I'm not set up to weld ( nor have I ever) welded aluminum.
 
That set-up would be strong enough for a 50.
However, 1 thing I would do is put a thin sheet of aluminum on each side of the plywood and cap it with u-channel. If the motor is just clamped to any transom and the clamps loosen a bit, the channel will prevent it from coming off. OR just bolt the motor to your jack-plate.

I bet it goes like a raped ape!
 
good call!!! I had planned on bolting in the lower two holes on the motor bracket. my luck though the plywood will snap in half an my motor will be in the sound... I like the aluminum "skin" idea.... I have some unistrut left over, I wonder If I could use that as the cap? :D
 
I have a new 20 hp Yamaha 4s on a 1448 flat bottom and it runs about 27 mph, WOT. There will be a lot of leverage on that, grab the top of it and pull or shake it fore and aft and if you think it is strong enough then it probably is, the angles are not a concern, more concern is the aluminum transom oil canning at the bottom.
 
surfman said:
... more concern is the aluminum transom 'oil canning' at the bottom.
Meaning if there is no 'knee' or vertical structure (typically on a 45-degree angle) that bears the thrust of the motor ... that 20hp could end up inside the boat by peeling the transom over on itself ...

I'd make sure that there was not only a good strong knee inside, but would add wood or aluminum channel or angle to inside the transom full-width. And regardless of what the plate says ... that a whole lotta HP on that 12' skiff :shock: !

FWIW I have an old '69 vintage Sears 12' tin rated for a 10hp and she goes like raped ape with an 8hp on it! One person that is ... but I sure wouldn't want more ponies on mine, as she's a very tippy 12-footer ...
 

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Ictalurus said:
This is the second time in as many days that I've seen what appears to be a "reverse transom" on a tin at the site.

There is no reason that would not work, you made one heck of a nice jack plate.

However, you have 20 HP on a 12' boat, it seems pretty wide, but there is a chance it may not be rated for that HP. I'd still keep both though, that's a sweet looking 12', and maybe for a winter project, I'd use a wider/deeper piece of ply and give the transom more support w/ that 20 hanging off the back. At that point, you could, or might as well, convert the boat transom to long shaft. Would appear you'd just need to add a few feet of channel over the new transom.


An consider tying it into the gunwhales. That will eliminate bending the transom - especially on throttle up.
 
In a couple of the pics, you can see a pretty stout support actually going to the seat. I don't see what it looks like at the floor, but that should be extremely strong.
 
Thanks for all of the feedback guys. i really do appreciate it. this boat actually does have a pretty beefy support and the aluminum is actually insulated. I believe there is foam in between the two layers of aluminum. I can put my bare feet on the bottom of the boat while I"m out in the puget sound and my feet barely feel anything colder than the outside temp. the rear of the boat feels almost as thick as the bottom.

here is a picture of the internal support going to the seat.
 

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another weird thing about this boat.

apparently this is not a welded or riveted boat. Although I do not see how, but this boat uses a patent seam I guess and they should never leak ( never say never )

https://www.duroboat.com/
 
troyschwab said:
another weird thing about this boat.

apparently this is not a welded or riveted boat. Although I do not see how, but this boat uses a patent seam I guess and they should never leak ( never say never )

https://www.duroboat.com/

Interesting! I have never seen anything like this. No welds, no rivets... would make me nervous but it obviously works.
shop1.jpg
 
troyschwab said:
apparently this is not a welded or riveted boat. Although I do not see how, but this boat uses a patent seam I guess and they should never leak ( never say never )

https://www.duroboat.com/
Wow, that's impressive actually! It's almost like the whole seam along its entire length is a 'riveted' entity, in that it is compressed along the full length.

Now I've NEVER bought a new boat, but if I were looking for a tinny to have for the next 20-years or so ... that design feature may just have buying one from them! Here's their write up about it:

The Durojoint - Strong and Leak proof, an Aluminum Boat that doesn't Leak!
The patented "DUROJOINT" system of hull construction was invented in Australia in the late 1970's by a welded boat builder who sought an alternative to riveted thin-sheet boats. The problem was that the Southern Ocean tends to be rough much of the time, and boats welded or riveted of thin-sheet aluminum did not hold up. Welds cracked and rivets loosened and leaked.

The durojoint proved its effectiveness both in skiffs built for ocean use, but also in river boats that are raced up and down shallow and rocky Australian rivers. In 1984 Duroboat commenced production in the Seattle factory The secret of the durojoint is that the compressive forces that shock the seams of an aluminum hull are dissipated along the continuous edge of the durojoint. Each seam in a duroboat is protected from external incidental damage by the heavy duty aluminum extrusion. The sketch below shows a durojoint chine and an early durojoint Keel. The modern keel ia actually a hollow extrusion with a bridge across the valley shown in the picture below. this gives the keel a double wall for even greater strength than the first durojoint keel.
 

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Looks pretty cool but I would be concerned about crevice corrosion, I wonder what they do to prevent that?
 
I finally placed the motor on the new mount. it appears that I miss measured just a bit. I'm thinking about grinding just a bit off the motor bracket to fit better. just a tiny bit. anyway, here it is.
 

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Before you cut or grind anything I would try it first. I run mine as high as I can, it will vent at times in rough water, just back off the throttle and she grabs again but I like the motor to be as high as possible.
 

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