Hull Bottom Profile Has Hook in Early 13-foot Boats

[mgajim]

On the 1967 13-foot Boston Whaler boat I had, I revised the bottom shape aft. [The hull bottom] had two molded-in fin keels that I cut down. The center keel was straight near the transom, but there were concavities port and starboard creating a natural trim tab to the whole transom, good for pushing the nose down at speed, but dragging the entire boat through the water. A yard stick held against the bottom at the transom will show the curve.

I filled the hollows and the boat picked up speed. My 33-HP Johnson could pass a 40-HP Mercury by several MPH. On the other hand, it became more unstable with a strong headwind. The boats had a record of blowing over with a strong facing wind, anyhow. Anyone else notice the bottom shape of the early boats?

[goldstem]

ALL the classic 13's had that hook in the bottom.

[jimh]

This topic has been discussed previously. See

http://continuouswave.com/ubb/Forum4/HTML/007445.html

http://continuouswave.com/ubb/Forum1/HTML/011953.html

http://continuouswave.com/ubb/Forum4/HTML/005062.html

http://continuouswave.com/ubb/Forum4/HTML/007236.html

http://continuouswave.com/ubb/Forum1/HTML/021129.html

The general consensus of the purpose of the hooked bottom was to help keep the bow of the bow from rising when transitioning onto plane. I don't recall any reports of anyone reworking the bottom to remove the hook, so your mention of having done that is quite interesting.

You comment that the boat became more unstable when running into headwinds seems to suggest the bow had a tendency to rise. Certainly removal of the hook in the bottom would tend to allow the bow to rise more easily.

Can you offer any observations about the tendency of the bow to oscillate up and down while on fast plane? This is usually called porpoising, and it has also been speculated that the hook bottom profile tended to reduce porpoising by keeping the bow down.

[mgajim]

You gentlemen have certainly covered this topic in the past. My boat had no tendency to porpoise or pound after I changed the bottom shape. It did skid in turns more. Weight balance was important. I understand the reasoning of the additional outboard engine anti-ventilation plate fin attachments but dragging additional mass through the water seems counter productive. I didn't particularly need to go faster, but a boat easier to propel is better on gas milage.