Long Shaft/ Transom Height?

[springbok]

I have a 14' Aluminum fishing boat, it has a 16" transom. I just purchased a 25hp Evinrude used at a really good price but I think it's a long shaft. Is this a problem? If so what can I do?<br />Also from what locations on the motor do I measure to determine if it's a long or short shaft?<br />Thanks,<br />Paul

 

[cvx35]

Re: Long Shaft/ Transom Height?

Refer to a topic about 5 or 6 down below your's.... the last reply will show ya a diagram about transom height.. topic is (1986 twin 50hp popping out of gear)

 

[oldboat1]

Re: Long Shaft/ Transom Height?

Hi Springbok -- Measure from the point the top of the transom contacts the mounting bracket, to the top of the ventilation plate. A regular (short) shaft would be 15". A long shaft is 20" (can be 25" for the bigger motors). You could run a longshaft motor on a regular-height transom, but not very well -- think there would be too much drag for the boat to plane. Unfortunately, you can't build a transom up 5" on a 14' aluminum -- maybe a jack plate would come close, but there is some expense with that.

 

[springbok]

Re: Long Shaft/ Transom Height?

Oldboat1--Do you really think it will make that much difference? I measured the transom mounting bracket to the ventalation plate and it's 18"...... That plate sits about 2.5" below the bottom of the boat.... <br />Thanks,<br />Paul

 

[OBJ]

Re: Long Shaft/ Transom Height?

Hi springbok...yes it will make a lot of difference.<br /><br />To much lower unit in the water creates a super drag on the engine and inturn causes the engine to lug until it gets on plane if it does get on plane. Problably what you will see is the bow of the bow go way up in the air and then come down....if it does. What you want is for the anti-cavitation plate even with the keep of the boat or no more than an inch below or above the keep.<br /><br />Couple questions....what year is the motor (model will do) and is the boat rated for the 25?

 

[springbok]

Re: Long Shaft/ Transom Height?

OutboardJim, it's a 1988 Evinrude 25hp, the boats max rating is 20hp (I figured since the only difference between a 20 and 25 is the carb it didn't really matter as they both weigh the same)<br />Thanks for the info...

 

[G DANE]

Re: Long Shaft/ Transom Height?

Springbok<br /><br />You are right about the weight and 20/25HP diff. I have seen this solved very easy by bolting a piece of 1 1/2" plywood around 20" high and 15" wide on external side of transom, adding the extra hight. Paint it well 3-4 times with ureathane paint, eventually primed with poly resin first. Cut the lower end in transom shape or whatever. Bolt your outboard to it, letting lower bolts go all the way through transom when it is mounted on transom. Use 2 1/2 or 3" screws for every 2" areound the edge, remember to seal holes in transom. This will work fine as we are talking of 25HP, not 250HP. You will go a lot faster and use less fuel, + get a lot easier on plane. If you are a little creative with figuring the best size and shape of plate, it can be done quite nice.

 

[rodbolt]

Re: Long Shaft/ Transom Height?

hello<br /> I run a 35 on my 14 and I have to place the plate about 1"above the hull. if its to low it will cause water to ride up the transom and fall in the boat. we build transoms up on duck boats like that all the time.<br /> good luck and keep posting

 

[waterinthefuel]

Re: Long Shaft/ Transom Height?

Spring, boats are not given horsepower limitations due to weight. They are given because that particular boat has shown to be safe up to that horsepower. You can't insure an overpowered boat, as well as your liability if you should hurt someone or damage property is 100% on your shoulders. There is no fighting it should it go to court.<br /><br />I have a little boat that's rated for a 40. A Tohatsu 40 weights about 165lbs, yet a Johnson 40 weighs in at well over 200. I couldn't dream of sticking a 230lb outboard on the back of a 13 foot boat with about 4in of freeboard at the transom with a 120lb 28hp engine. I personally wouldn't put a 40 on my boat because I feel it would be overpowered. It's on that borderline with it's current powerplant.<br /><br />My point is, be careful with that rig. Its overpowered (admittedly not by much) but it is. I am someone who likes to take things very carefully and do things as safe as possible. Overpowering a boat isn't high on my list of "safe" things.<br /><br />Just don't kill anybody. We want you, and everybody who fishes around you, safe and sound and casting like maniacs.

 

[oldboat1]

Re: Long Shaft/ Transom Height?

You might test it out on the boat, and check out the performance. Weight is probably not an issue, provided the transom is in good shape (You can stiffen it a little, by the way, if you put a metal plate under the transom screws on the inside.) I think you might not be able to get on plane, and the torque in trying unsuccessfully to do so will put additional stress on the transom --so be careful. If you want to use the boat at slower speeds, the longer shaft length will probably not be a hinderance -- and in the meantime you can think about ways to mount the motor higher (or look around for a short shaft to fit the motor). The older motors have a 5" extension in the leg that provides the longer length. In these motors, you take out the extension to make a short shaft -- provided you have a shorter driveshaft that will work. On some that I have, I convert to a short shaft by simply bolting up a spare lower unit with its drive shaft in place (which is how you would normally purchase a used lower unit).