BYYB Forums

Greeting all,

Does anybody know what the maximum safe horsepower is that can be applied to a Weekender transom ... assuming that the motor mount is up to the task?

I'd ask my power boat friends, but they would suggest something like this ...

[attachment=1]

Cheers,
Tom

That's neat Tom, and I thought having a pair of engines on a power boat was practical. No fear if an engine packs it in out on the big water with that baby. Bad fuel supply could trash the whole lot though.

I can't speak for the Weekender transom. During my vacationer build, I doubled the 1/2 inch plywood on my entire transom. I've had no issues with my 9.9HP Merc hanging off it so far. I'd suspect that a stock Weekender transom would likely support up to a 5HP safely. I'll let other Weekender builders chime in on this one.

Greg

You really can't use much more than about a 4HP outboard.  Not from the wieght or vibration point of view but more from what is practical from an application point of view.  You will only be able to get to hull speed and you can accomplish that with a 2 1/2 to 3 hp outboard.  I know of one with a 9 hp on it but it is far too much of an engine for a Weekender.

A whole lot depends upon how well the entire mount issue is addressed.  Doublers behind the thru bolts and a antivibration mount will help a lot. 

I wouldn't haul with it mounted in any case. 

One inch additional ( 4 x 1/4" ply) behind the motor mount on a Vac allows trailering with a Honda 9.9 electric on the back.  Wkndr ??

I have a 5 hp that I hang on the back of my Weekender but rarely use it over about 1/2 throttle as it doesn't go any faster just uses more gas and makes more noise.

My Pocket Cruiser transom is over built, not that I need it but it makes me feel better. I had a friend who pushed his transom in and had to run aground to keep from sinking. Long story, adult beverages involved. I have  a 3 1/2 hp and a 4 hp and both will get me to hull speed at half throttle or less. I still take the moter off when trailering the boat. The moter sticking out behind the boat bouncing down the road makes me pucker, if you know what I mean. Bud :

I guess I need to qualify the leaving of the motor on the transon whe traveling.  My trailer was custom built to provide support  beyond the transom.  I had about 6" of bunk extending behind the last of the wood so I didn't have a bending moment inthe hull.  If not for this extra, full length support that motor would not have had the structural  support necessary for highway speeds even with the 1" backing.  104lb on a 36" lever is a hell of a lot of stress.

Weekender's hull shape will only accept a total of 2 HP (actually less then this) to drive it to it's theoretical hull speed (4.8 knots). In a good breeze, she can make a little over 5 knots, but then you hit the wall of drag, associated with hulls shaped like this and you need literally dozens of more HP to go any faster. Therefore a 5 HP is more then enough power to punch through the worst of chop and still maintain speed.

Vacationer has the same hull shape issues (typical of all displacement boats), but her longer LWL permits a hull speed of 5.7 knots and she can see 6 or slightly over it in a stiff breeze. There's a lot more drag to Vacationer, but 10 HP is more then enough to shove through chop. 5 HP will do fine on a Vacationer, though there could be times (not very often) that you might want a little more "punch" to the engine.

Both Weekender and Vacationer have a stock designed transom that can take the weight of a small 2 stroke outboard (5 HP or less). 4 stroke outboards have changed this considerably. A Honda 9.9 is about a 120 pounds, which is a lot more then a 10 HP 2 stroke, which typically will be around 80. The same is true of smaller 4 stroke engines. This means you'll probably want to install a backing plate.

On the inside or the outside of the transom a good piece of marine grade 1/4" plywood will do up to 5 HP. If using cheap plywood (3 plys), then increase to 3/8". If using a bigger engine (up to 10 HP) then 3/8" marine plywood is fine, again if it's cheap stuff, then up to 1/2" because of the limited ply count.

If installing a big engine, you also may want to install a knee on the inside on the transom. This could be a piece of plywood, set at a 45 degree angle (the grain) and well boned to the transom and bottom planking. Making two, one on each side of the backing plate would really be stiff and fairly easy.

Bond the crap out of the backing plate and the knee. A good bond will insure the loads are transferred from the engine mount to a large portion of the transom and most importantly the hull bottom.

On a trailer, it's best to either remove the outboard or install a "transom saver" rod. I've made dozens of transom saver braces over the years. It's just a rod that has a V notch on the one end to receive the lower leg of the outboard and a socket on the trailer for it to fit into. This keeps the engine from bouncing around and twisting the engine mount right off the boat (I've seen this happen at 50 MPH, not pretty, but funny as hell to watch, if it's not your boat).

A transom bracket adds more leverage to an already difficult situation. If using a transom bracket, up the backing plate and knee thicknesses by the next size plywood. Use plywood or metal as the backing plate, not solid wood. Plywood's construction helps transfer and disperse loads better then solid wood and is much more dimensionally stable.

Craig, I'm a happy camper, I've got a new roll of duct tape . . .

Hoser!  8) 8) 8)

Thanks everyone.

I am just about to put the sides on the boat and now is the last opportunity I will have for beefing up the transom.  Since I live so close to big water (Lake Michigan is an inland sea without the salt) I know the boat will eventually be sailed out there, and I'm not going without an engine to get me back.  With a 2 hp requirement, it seams like a simple backing plate is all I need.

I had my eye on this little beauty ... http://www.tackletour.com/reviewhondabf2d.html



which is a Honda BF2D 4-stroke 2hp engine that weighs only 27 pounds, exceeds EPA 4-stroke requirements, is air cooled, has a centrifuge idle clutch, and swivels 360 degrees in its motor mound so backing up is not a problem. It should cost about $750 new.

Duct Tape?

Is there a new motor mounting technique that I am not aware of?



Cheers
Tom

P.S.  About the only thing that Duct tape should NOT be used for is sealing duct work.  For that you need an a special aluminize tape.  (by law in California)