Motor mount/transom question

Rob406

Petty Officer 2nd Class
Joined
Jun 11, 2012
Messages
108
Hey everyone, I recently acquired an old '61 (I believe) Duratech 15' aluminum in rough shape. I've since repaired several holes to the point that the boat now holds water when filled from the inside. I've got my hands on a 50 hp force motor and need some advice before mounting it. First and foremost I intend to replace the transom with new wood as the existing one is very soft. That being said the motor mount is quite a bit wider than the transom (Don't have dimensions off hand but can easily take measurements later tonight after work) I'd say about an inch, inch and a half difference at least. What is the best way to go about fitting the motor to this boat? Would I simply build out the transom with extra wood, or is there a better way to go about this? Any advice will be appreciated, I am hands-on, and automotive experienced, just new to boats and boating. Thanks for reading!
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,585
:welcome: aboard baker...

I have never replaced an aluminum hull transom, but I can't see it being much different then a fiberglass version. And with that stated, I would research transom builds on these forums and read some of the others that have done this before. I would think your transom needs totally torn out and a new one built up from quality exterior plywood and probably two 3/4" pieces as well laminated together to give you that added strength you'll certainly need with a 50 HP OB engine hanging in it... Others with absolute knowledge about aluminum transom replacements will chime in and give you better ideas I'm sure... JMHO!
 

Tnstratofam

Commander
Joined
Aug 18, 2013
Messages
2,679
Pictures of your current transom will help. I would say replacing your transom with a wider one is possible. I wouldn't add to whats there now. I would replace it with one solid piece. Two pieces of 3/4 marine grade plywood or two pieces of good exterior grade plywood sealed with epoxy with a uv inhibitor would be fine. Glue the two pieces together with a good waterproof glue like Titebond III. The plywood can be sealed with spar varnish or woodonglass's old timers wood sealer as well.
 

Woodonglass

Supreme Mariner
Joined
Dec 29, 2009
Messages
25,924
Some Aluminum boats have inside outside wood transoms. That means, One layer of 3/4" wood is Mounted on the inside of the aluminum skin and the other layer of wood is mounted to the outside of the aluminum skin. Others use just 2 3/4" pieces of Plywood laminated together and mounted on the inside and incorporate an aluminum cap over the top which must be removed in order to get the new transom in place. Some have knee braces to give additional strength to the transom. As tnstratofam states Pics would really help us to "SEE" what your working on. Does the Transom corners have caps?
 

Rob406

Petty Officer 2nd Class
Joined
Jun 11, 2012
Messages
108
Hey guys, wow thanks for the fast responses. Maybe I need to clear up my previous post. The "c channel" part of the motor mount, the uppermost extremity of the mount, which would sit on the very top of the transom, is 3 1/2" wide. The transom is only 1 1/2" wide -- two 3/4" pieces of plywood, they are sandwiched over the aluminum, one on the inside, one on the outside. Below this, at the bottom rear seam of the boat, there are three 4x6 90* gussets hard riveted on. I don't intend to modify this design in any way other than to just replace the old wood (and at which point I will certainly be asking what type of wood, sealer, etc, etc). So back to this 2" difference...Do I need to accommodate for that in any way, or am I safe to just go ahead and mount the backside flush against the transom with the four bolt holes in the motor mount?

I'll get some pics up in a few but hopefully you guys know what I'm trying to get at here....
 

Rob406

Petty Officer 2nd Class
Joined
Jun 11, 2012
Messages
108
No Title
 

Attachments

  • photo221713.jpg
    photo221713.jpg
    25.5 KB · Views: 0
  • photo221714.jpg
    photo221714.jpg
    25.9 KB · Views: 0

Woodonglass

Supreme Mariner
Joined
Dec 29, 2009
Messages
25,924
Sooo, what you're saying is on the motor, the mounting "Throat" is 3.5" wide??



If that's the case then, I'd just fashion a spacer block and move on.
 

Rob406

Petty Officer 2nd Class
Joined
Jun 11, 2012
Messages
108
Exactly. Good enough then. Thanks for the response. Sorry my boat terminology is lacking (working on that). Why, then, just out of curiosity is the mount made that wide? Also do you guys foresee any reason why a 50 on this boat would be too big or anything like that? As previously mentioned I think the transom design is definitely capable enough but I do know from lifting it that the motor is pretty damn heavy. Just working with what I have available....Still quite a bit to do. Used about 3lbs of aluminum wire trough a spool gun to patch all the corrosion holes, also sectioned the three main ribs underneath the boat and flushed with water, each held about a pound or more of sand and salt mixture which I assume was causing the corrosion. I had a difficult time welding on this boat as for one I'm new to aluminum and also it was very difficult to get this metal anywhere near clean enough. I intend to put forward controls in this boat and also fabricate a hood with a windshield, etc, on a budget of course, so it should be a little heavier at least when I'm done. All I have to work off of is pictures, it looks like people are running 40-50s on these but it's hard to tell.. Any info will be appreciated. Also I'll be hitting you guys up again in the near future most likely for transom info, sealants, etc.
 
Top