Moesly Seacraft 21 repower opinions

[Bushwacker]

Originally Posted by SandlapperGT

. . . I don't think (and I may be way wrong) that the SC 21M was every considered a speed demon, but that it could maintain higher speed in rough ocean conditions.

Merc did a bunch of tests at Lake X back in the 60's and found that the VDH hull was about 10% faster than a conventional constant deadrise deep V of the same weight and horsepower, so the early SeaCrafts had a reputation for being pretty fast boats. What is really amazing is that all of the Moesly designs, if powered with the engines they were designed for, seem to be able to plane at about 12 mph! Don't think a similar vintage Formula, Bertram or Donzi will even come close to that!

I spent a lot of time under the 20' hull when I painted the bottom on my boat, and discovered some subtle details that show how brilliant Moesly was as a hull designer, despite no formal training as a naval architect:
1. The outer panel has a slight wedge built into it in the aft 10', which you can see if you sight along the chine back toward the transom. This helps the boat get on plane at low speed.
2. Since the hull develops more lift as speed increases, the hull rides higher in the water at high speed, so the outer panels are almost completely out of the water at about 40 mph. This means that the wedge built into the outer panels does NOT limit max speed as it would on a constant deadrise design.
3. Since the inner panel is carrying most of the load at high speed, Moesly incorporated a little bit of rocker into the inner panels, which allows the bow to rise at high speed to reduce wetted surface for less drag and more speed! If you look at the Boating Magazine test of the 20' Seafari in the Literature section, you'll see that sure enough, the running angle increases from a very flat 0.5 degrees at 32-36 mph to 1.25 degrees at almost 40 mph! I've noticed this in my own boat and think it's an absolutely brilliant design detail that very few people are aware of!

As for "not being a speed demon", what you have to remember is that the outboards available in the early 60's were fairly small. Moesly raced the early 21's with a pair of 110 hp Mercs which is why he didn't run much over the mid 40's. It's actually a pretty fast hull if you add more power, and I think Island Trader has seen well over 50 mph with that 383 stroker motor he put in his 21! But you're right, the boats rode so well in rough conditions that Moesly was very competitive with and often beat 30' inboards running twin 500 hp I/O's! And most of us that run offshore are more impressed with rough water speed capability than ultimate speed in flat water!