Boat Design

Hi,

I am a designer (Filipino), working with an American guy, who has a simple goal (his simple is never simple but is definitely challenging) and I would appreciate some feedback. So here's the story. The Philippine gov't has a program where it is introducing (very slowly) US$1400 barebones fiberglass skiffs if they can get a loan (most can't).to fisher families as we call them here (plus the boat can be used for tourists and possibly even economically hauling small freight between islands). So what is my problem....(and the American says a lot of you will scream)...it's designed as semi-displacment hull, 17 ft. long, that can sail.....and / or take an outboard or inboard. The estimated weight is 800 lbs with a small inboard diesel unloaded (no people, ice, gear). Loading could add 900 lbs (and yes we caculated all including fuel and water). It's made of hardwoods (almost all mahogany framework) and 1/2 inch marine ply. The hardwoods versus software woods perhaps used in your country) provide a lot more strength and naturally dimesnionally can be smaller. So what are my questions? The stern of the boat has (underneath obviously) X feet of almost flat surface with the thinking being will it plane with the dagger board up? What horsepower would be required in an outboard versus an inboard gas or inboard diesel? The bow is more convential with it resembling the bow of a typical single hull outboard family type ski boat (and given that you can guess that what is "under" does not resemble a "plow:"...displacement hull. BUT BUT BUT ....we have angled up the edge of the vessel....a distance of XX inches like this..."/" before it joins the side....(try to imagine two waterlines...one for "plowing" and the other to assist in sailing as well as planning . If anyone has thoughts they would be most appreciated. I can also send a copy of the drawings or put them up on SketchUp. Thanks in advance for any thoughts......no matter how small. We think we are on target but would like to not have to tear it apart and start over. Note.......we will use Epoxy resin on the exterior and fiberglass where we have joints and seams. It may not be the prettiest when done but safe, waterproof and functional. Winds here in the island are 6-14 knots typically FYI. And if you want a free place to stay when visiting the Philippines your information buys you free room and board (rice at least 2x a day though...hahah). Thanks, Josh....

 

Hi Joshua
That's a very detailed coverage of the project.

I have been interested in motor/sailing combination boat for many years, so your problems strike a chord with me. There have been many discussions over the years on the topic.

One decision I made early on in my design process, was to make the power propulsion more important than sailing in the hull design.
The difference between an average sailboat and a well designed sailing hull at 17ft, is at most 2 or 3 knots.
However, a hull design that improves motoring could be an improvement on 10-12 knots, which is far more significant.
For a 17ft boat, you would have no trouble planing with a 40 HP outboard.

In any event, a copy of the design can be posted here if you use the "Upload a file" button, and I think that it is going to be important for any sensible discussion.

A good place to start would be by looking atattach the worlds most successful small motor/sailer , the Macgregor 26 MACGREGOR 26 HOME PAGE http://macgregor26.com