Shorter OB15?

[Callumh]

In the "read this first" section it mentions that you can adjust the length of the boat by 10% but it may require redesigning. I was wondering if the OB15 could be shortened to something like 14 or 13 1/2 ft. I assume it wouldn't be too complicated but i'm new to boat building so I would very much appreciate some professional advice. I own a 15hp merc 2 stroke which i picked up as i found a good deal on it and knew i would eventually get my hands on a little boat (really want to build my own boat now). I love the look of the OB15 but would like to build it a little shorter so the 15hp can push it along at a decent speed.
Thanks
- Callum H

[OneWayTraffic]

Generally boats can be scaled in all dimensions by not more than 10% for a powerboat. If increasing size and therefore HP, there is often a requirement for some extra glass on the bottom panel, overlapped to sides and transom.

For your case scaling a boat only in length will screw up the panel development. They will no longer fit each other very well. If experienced in boat building methods you could still get it to work, by checking measurements off frames etc. Another option is to extend/remove a slice at the transom, where the boat is a more straightforward shape. One experienced builder has done this to extend a C19 to 21'.

In any case it's a lot of work and no guarantee that you will have a boat that performs well. In any case I am doubtful that shortening the boat a foot or two will have any effect on speed. You will lose planing surface.

Worse case you take a lot longer to build it, get a worse product and don't gain any speed. If this is your first build you can fully expect your boat to be heavier than designed.

I would strongly advise that you either build it as designed and find a 25 or 30hp motor or build the FS14 instead. The FS14 will perform well with a 15hp.

[TomW1]

Downsizing the OB15 takes a lot of work for a first-time builder. If you downsize in one direction you must do all directions. By the time you are done doing it you will have a smaller boat than the FS14. I strongly suggest you look at the FS14. Your 15HP will work fine on it and there will not be nearly no difference in looks between the downsized the OB15 and it.

Tom

[jacquesmm]

Two good replies above.
If you scale, scale all dimensions. It will be much easier.