Beam increase

I am thinking of building the FAO boat. I want to put a small light weight sitting headroom cabin on it similar to what is on a Redwing 18 or Ninigret. I would maintain the tiller steering and all other design features of the boat. The problem I see is the limited load capacity of the boat. 350 kg for the 20 ft version that I want to build. There is provision in the plans to Incease the beam by up to 20% and I am wondering how much roughly doing this would increase the load capacity. I know it will affect the efficiency of the hull horse power wise but I have a 9.9 hp engine already rather than the 5 to 8 recommended. Also is there anything to be gained other than weight and work by adding 3 or 4 inches to the depth of the boat either by adding a coaming or directly to the sides. I appreciate any insight you all can give.
Mike

 

If you only increase the beam, the load capacity will increase by about 20%. The design, as published, is very refined. I think that a different boat may be more adequate for your needs. What you are adding in weight for the deck, house and extra freeboard will negate any gains on the extra beam. Also, the beamier boat will pound more and use more fuel.

 

Any recommendations on a similar boat? Displacement hull around 20 ft long not stitch and glue but ply on frame. Low horsepower outboard with a small sitting only cabin. Capable of running out of my local harbour into the sound. Think 20 to 30 kn. winds with a steep fairly high chop. This is the norm here outflow in the morning inflow in the afternoon. I just want something to go prawning and crabbing. It rains a lot here that's why I want a little cabin so my wife and grandkids can shelter when they've had enough of wet.

 

30 knot winds ? Surely not. I'd say 15 knots is about the limit for small boats in open water.

 

Well I don't choose to go out in 30 kn winds but one can rely on it blowing up when you are out there sometimes. Squamish is notorious in fact the word Squamish means mother of the wind in the Squamish language. I've come home more than once with a double reef in my little 23 ft sailboat. Or sailing on just the stay sail or even just the storm jib. I have to plan for it. It would be plain stupid not too. The plus is we are the number one place on earth for kite surfing if you are into that. Those guys love 30 kn winds.

 

Sounds like an uncomfortable and possibly unsafe experience in a narrow little boat.