River Boats Questions...

[Underhill]

I am considering building either the 23 or 27 ft river boat as per your plans but I had a question or two.

First, I plan to use it on some local small lakes but we also spend a fair amount of time on a seaway (The St Lawrence on the border of NY and Canada) that at times has a fair current of 3-4 knots (I'm guessing) in the narrows. I've motored through there in a sailboat and we were barely moving thanks to a deep draft and a barely adequate motor. Is it safe to assume that with the shallow draft your boats would not have a similar problem?

Would a slightly larger motor help? Say 15hp vs 10. I'm relatively new to motoring having spent all my limited time on sailboats.

Thanks a bunch,
Underhill

[Boatmik]

Howdy Underhill (and a big Welcome!)

That is the decision I would make too if in doubt. The cost difference between the two outboards is not very great - the geared down Yamaha High Thrusts are the ones to go for.

Generally boats will be affected in proportion to their speed. 15hp is going to bring the sustainable higher cruise speed up from 6 to 7 knots to a knot or two more. It will have the bigger effect on the bigger boat (the 27footer vs the 23footer).

You just have to the the math(s) (we add an "s" in Australia).

If you have a deep keel boat with a motoring speed of 5 1/2 to 6 knots you are left with 1 1/2 to 2.

Not much extra.

But the riverboat at 8 to maybe 9 gives you 4 to 5 over the ground. At some cost to economy compared to the yacht ... but fuel is almost in proportion to the number of horsepower you are using right now.

As far as the more open water goes ... I hope you have read my caveats on seakeeping and waves on my webpage for the 23ft Dayboat/Launch. The longer boat will also be easier to steer with following chop.

The back end of the interior of the 27 footer should be re-organised to suit your needs. That head (toilet compartment) is way too big!!! Move it to the back corner and put a seat down along the opposite side I think.

I can help you work out that part and keep or improve the structural design if you wish.

Best wishes
Michael

[Underhill]

Thanks for the quick reply.

Yeah I would rather build the longer boat. I can't imagine the cost and time investment would be that much more. My primary concern is workspace. I have a 22 ft long garage space so even the 23 will be marginal (working with a small portion hanging out the doors).

As for the necessary changes, I don't imagine that will be a problem as I'm an engineer. I thought about designing my own boat but while I can do the math and autocad work, I have zero experiance with boats. I've drawn a few but worry that I'm missing something.

Realistically it will be March or April before I can get started. But I tend to over investigate everything...