My homemade transom extender

[Merc25XD]

After a ton of research, I came up with this simple design. It fits on the back of my 14' Lund. I had my 6hp Merc on the back end all season but then a month ago, I bought a 1985 25hp Merc long shaft. (I couldn't pass up the deal). The aluminum is 3/8" angle stock, the plywood is 2-3/4' pieces screwed/glued together. I need to drill the last 4 holes to attach the unit to the old transom. It seem sturdy enough to hold my 25Merc. ALL metal parts are either aluminum or stainless. ALL comments are appreciated.

 

[Fenwick2]

Re: My homemade transom extender

Nice Clean Job.

 

[Evinrude15]

Re: My homemade transom extender

Do you have a merc 25 XD?? If so e-mail me at gillfish13@hotmail.com. my name is cody. I want to ask tec questions about it. Mine just wont run right even though I have rebuilt it, cleaned carbs, ETC. THANKS!!!

 

[Merc25XD]

Re: My homemade transom extender

I have read that the cav plate should be level with the bottom of the boat for best performance. The measurement on my 25hp Merc from the mounting bracket (bottom side) to the cav plate is 21 1/2". My new higher transom will give the cav plate measurement of 21 1/2" . Should work.

 

[Merc25XD]

Re: My homemade transom extender

Mindblock...thanks for your input. I have considered doing just that.

 

[jbjennings]

Re: My homemade transom extender

JMO---I have an '84 merc 25xd and the angle brace is a good idea. Those rascals have a lot of torque and will tear up a factory transom if you beat on it like my dad used to do. The corners of the transom braces might crack also if you don't use a "transom saver" on it while you're trailering (they did on mine). If you like fast motors you ought to enjoy it--my 30hp johnson on a 1542 johnboat won't keep up with it on my dads 1536 johnboat. I will try to answer your questions but I almost bet that I can't, but it will be childsplay for some of these mercury guys. I've rebuilt the carb twice and no matter how I adjust it, it will idle but not as smooth as I'd like. I'm certainly no merc mechanic by any stretch, though.
by the way, that is nice craftsmanship, and looks good, too.
JBJ

 

[Willyclay]

Re: My homemade transom extender

That's great looking fab work. I'm not an engineer, just an old guy who has been fooling around with boats and outboards since I was 10 years old. What I have come to appreciate more in my later years is the tremendous forces generated by outboard motors on transoms of boats. I have cut transoms down for short-shaft motors but never extended one. Regardless of the opinions found here, the only way you will know about your design is to test it. Be careful, add a safety chain to the motor and work up to WOT in several RPM steps to verify everything is doing what it should. Good luck and let us know how it goes.

 

[Lakester]

Re: My homemade transom extender

hello 25xd~

nice work! looks engineered for sure! have u considered going into the boat building business... or at least Lite Tanks?

with the 4 3/8" angled alum support brackets i would venture a guess from my background you will have MORE than enuff vertical structual integrity. what i would do however, if it was mine... is to use larger bolts than used on top. and i would use large washers on front and back. and i would use 3. top looks to be 3/8? so id go to 7/16 as a min. also would seal the new wood and the thru hole if transom is wood. look at O&G pressure vessels, and rivits on aircraft, etc... they use many and closely spaced.

many times re-designs exceed structural limits of original design. so what worked ok then may not have the same life as the mod. if it were mine, until i had determined the overall strength [no dobut u exceed boat transom's, even factoring in the new leverages] i would simply avoid hole shots. bring in the power slow and smooth. thus the loads can transfer on down the boat's sides, and hull, etc.

regards
lakester

 

[tashasdaddy]

Re: My homemade transom extender

this is mine, again 3/16 X 3 inch stock in a sort of Z, for my 40 hp. iwould have done as your's is but i want to keep splash well.

 

[Merc25XD]

Re: My homemade transom extender

Thank you all for your comments......That's why I like this board...so much knowledge here. Lakester, thanks for your input. I will be cautious in the spring to see how things go. There will be NO hole shots. I just want to get to the other side of the lake a little quicker. I'm 66, so I have time to fish a lot.
Willyclay...I am a firm believer of motor safety chains, I use them all the time.
tashasdaddy...I have looked at your pictures for hours trying to decide if I wanted to do the same. I like your set up. I will finish mounting the new transom in the spring and go from there. Thanks again everyone.....wjw

 

[BF]

Re: My homemade transom extender

Nice looking job... Here's my $.02 since you asked.... have you thought about having the wood go the whole width of the transom? Basically make the whole width "long shaft" height? You could seal it in there with 5200 and it'd increase your freeboard at the back by 4+ inches. My other thought was that I might be inclined to run the angle on the inside down lower, and then add an aluminum spacer between it and the existing transom to fill in the gap where the transom is thicker higher up. Maybe it's not needed, but it would spread the load out more over the whole height of the transom instead of just being on the top 4".

Anyway, I've never done this project myself, but may end up in the future... used short shaft 4 strokes seem to be hard to find. Thanks for sharing your pict's... maybe I'll be looking them up in the future if I find myself undertaking this project.

 

[Chris1956]

Re: My homemade transom extender

WJW, You have done a nice job. Just so you know, a Jackplate performs the same function as your transom extender. Jackplates are frequently made of four pieces of angle iron, which are bolted together in pairs to form two U-s. Sometimes thay have wood between the U. The only advantage a Jackplate has over your design is that it is adjustable up and down, and the setback gives a bit better performance.

 

[Merc25XD]

Re: My homemade transom extender

BF..thanks for your comments. I did think about a full transom fix, but elected to try this idea first. If, in the spring, I find out that my design is not strong enough, I may try a full transom job with plenty of reinforcement. My current transom elevator weighs 12 lbs. I am sure that a full transom job would weigh considerably more...maybe 40+ lbs. I still like Tashasdaddys design. I'm sure it would work on my boat.

 

[Merc25XD]

Re: My homemade transom extender

Thanks Chris1956.....I looked at jackplates too. A little too expensive for me. I almost built one using "C" channel aluminum stock. I just looked at the transom on my 14' Lund. It is a very well built transom. I feel confident that my extension will work fine. I will just have to wait til spring to find out.

 

[deejaycee_2000]

Re: My homemade transom extender

good job ..... I also made my own ....

 

[tashasdaddy]

Re: My homemade transom extender

DJC, nice work.

 

[Merc25XD]

Re: My homemade transom extender

BOY...that extender is beautiful.......what size motor will you hang on there?
What size boat? Is it stainless?...Very nice job.....wjw

 

[deejaycee_2000]

Re: My homemade transom extender

Thanx ..... yep stainless steel, it was intended for my 8,5 ft inflatable, I wanted to try fit my 50hp yamaha race motor on there, but I get too much cavitation, so I did try it, but what a mission to get it on plane, it keeps on blowing out, my 30hp suzuki just works better on it .....

 

[MrBigStuff]

Re: My homemade transom extender

Let me add to the admiration and accolades; that SS extender is a work of art!

 

[texasbowhunter40]

Re: My homemade transom extender

Anyone got pictures of a transom elevator like the stainless model already installed.

Im looking at going from 15" to 20" transom on my 14' aluminum Smoker Carft Sea King