# Calculating bilge board/keel area

Discussion in 'Boat Design' started by hospadar, Jan 24, 2012.

1. Joined: Apr 2011
Posts: 63
Likes: 3, Points: 8, Legacy Rep: 30
Location: Michigan

I'm planning my new small boat after the untimely demise of my ill-fated first boat (http://www.boatdesign.net/forums/sailboats/hull-shape-simple-sailing-scow-37499-3.html#post490323)

This time I'm thinking to build something like a PD Goose, which is basically a 12' long PD racer (a boxy 4' x 12' scow type boat).

I'd really like to use bilge boards or some sort of fixed keel instead of a dagger/center/lee board. The reasons for this are:
a) less separate parts/moving parts to haul around/maintain/mess with while sailing
b) acceptable in shallow areas (most of my boating is inland lakes)
c) I don't really care about sailing performance all that much, just needs to work
d) no trunk in the middle of the boat

The boards will probably look something a little like this: http://www.pdracer.com/keel/195.jpg (perhaps not full-length, but they will just be part of the sides extended below the bottom of the hull)

My question pertains to calculating the area and placement of the boards, I assume the sail-area-to-underwater-foil area calculations I'd use for a daggerboard or leeboard still apply to bilgeboards, or will it be different since bilge boards are so low aspect? How will those calculations change because I have two boards (one on each chine) instead of a single board (should I just split the area between the boards?). Would the length of the boards matter all that much (the difference between full-length or 2/3 or 1/2 or 1/3)?

I'm pretty sure I could just wing it and it would work OK for my little boat, but if there's a better way, I'd be interested to hear about it.

Also, worst case scenario, the bilge boards suck and I hate them, I chop em off and use a leeboard, no real loss there.

2. Joined: Apr 2011
Posts: 63
Likes: 3, Points: 8, Legacy Rep: 30
Location: Michigan