Dura-jet outboards?

[Dougster]

Since I'm building the LB22 as well, this is of course a topic of great interest to me. Unfortunately I know almost nothing of outboards, other than a long ago 15 hp Sears beast that was miserable, and a 90 hp Johnson 2 stroke that was flawless. Right now I've been looking at the Honda BF30. To me the following things are of import:

Quiet
Power Trim/Tilt
Quiet
Easy Maintentane
Quiet

Oh yeah and it's gotta fit! Height of the power head is important I think, to look right. How's it going Eric? You fine tuning the jig? I think I'm calling mine good 'nuff but who knows. I'm looking for a good batten today to draw the hull panels.

Slow go Dougster

[MadRus]

Dougster,

About power heads, I think that Jacques designed this boat for a 20" standard shaft motor. If you go with a 15" short shaft, I think that gives you more room under the hood- you just make the transom cutout lower and that lowers the power head by 4-5". Is my thinking right on this?

-Dave

You can get all sorts of prop guards and cages for lobster boats and outboards that will help you save some money on prop replacement. Power and efficiency are another matter. Around here, on inland lakes and ponds, millfoil grows right up to the surface of the water and fouls everything. I'd hate to have to clean it out of one of those "jet" things.

[bear]

Have a look at this thread :

http://gallery.bateau2.com/forum/viewto ... ght=#58783

bear

[Dougster]

Thanks for the thread Bear. I'm not much leaning toward a jet. In my area shallow is good but this is no flats boat and I'm not going to be silly and try to make it one. I hit every reef in our bays with my SS prop when I fished my 18' bay boat with 90 horse Johnson and never had a problem so I don't worry about it.

Madrus---you bring up a great idea it seems to me. With the false transom protecting the stern, why do I need to worry about notching the true transom deeper to handle a 15" short shaft? Seems like no problem, and leaves options open so the lines aren't goofed up with a big tall motorwell hatch. If folks have thoughts on this I hope they weigh in.

Moving along Dougster

[MadRus]

Hmm... I'm not sure about that. You need to have the motor in the water to a certain depth for proper running- without cavitation. So, even using a 15" short shaft motor, you'll have to cut the transom down to get the prop in clean water, not to mention there's a large skeg on the bottom. I was just saying that the short shaft will give you extra clearance above the transom mount line so even if it were an oddly large power head, it would still clear with the standard collar and hatch.

[Boomer]

why do I need to worry about notching the true transom deeper to handle a 15" short shaft?

Generally speaking, the nose cone of your motor needs to be in "clean" relatively undisturbed water, which comes out beneath your hull. You transom is built so that you motor can do this.

There are special high performance situations where you can run the motor higher.

Also, your water pickups for engine cooling are right under the cavitation plate. The higher you have the cavitation plate, the more risk you take of burning up your motor.

[Dougster]

Yeah I get that. I was looking at the new Honda BF30, which comes with the 20" or 15" lower unit. The boat's designed for 20". I'm a bit timid about it but if I cut the transom down 5" and used the 15" lower unit it seems to me the cone and water pu's would be where designed, with the power head 5" lower. Still, I would be nervous about cutting down the transom that much I guess.

Finally got the jig built Dougster

[MadRus]

Hi Dougster,

Jacques' boat plans usually include a note about being designed for a 20" standard shaft motor, but a 15" short shaft being an option. You should just double check with him about it. It might mean lowering the motor clamping board, etc., but in general, it can usually be done without problems.

You definately have to have that motor running in "clean" water in my opinion to maximize the performance of the hull, especially with it being in a bit of a tunnel and with that skeg. Also, to make sure you keep things as quiet as possible while underway. An engine mounted too high is going to be a lot louder than one at the proper depth, especially with through the prop exhaust.

Also, it's a good idea, although not critical, to make your motor selection before assembly of the boat, so you can get an actual measurement off the motor of where the transom cutout should be. Some shafts are longer than others by as much as an inch and a half. In other words, a 20" shaft motor may have an actual shaft-length of 21" or 19", which means you have to make your cutout a little deeper or shallower depending on which motor you buy. Mine was a bit longer, so I had to add a block to get the anti-ventilation plate up about an inch- to where it needed to be for proper running.

[Dougster]

Well thanks for that advice. I had not thought of selecting the motor so early, but.... There is a honda dealer 45 minutes from my place, so maybe I'll take the first rainy weekend and make "field trip" for some info and specs. The website doesn't give good enough detail. I'll just take a tape measure It just doesn't feel good cuttin down the transom so much, but I gotta think it through. Don't want unnecessary noise and spoiled lines if avoidable.

Thankin' you for the input Dougster

[Cracker Larry]

I second the motion of choosing the engine before building the boat. Even if you don't buy it, choose it and go to the dealer and measure it. Measure from the clamp where it rests on the transom to the anti-ventillation plate, and from the same point to the mounting bolt holes. This will insure that your seat does not end up exactly where you need the engine bolts

Each manufacturer has different terminology for shaft length. And that may vary with different HP. It may save you some grief to measure before you build.

Also, given a choice I'd go with a longer shaft and higher transom. It is just more seaworthy. Keeps the waves from coming over the stern. I'm running a 25" long shaft on my GF 16, which is actually 23.5 inches from clamp (top of transom) to anti-vent. plate.