1978 Seacraft 20MA newbie

[Ironmanangler]

Just wanted to post the new project. I've been on this forum always browsing tempted to rebuild my own Seacraft. I came across an opportunity and jumped on the rare 1978 Seacraft 20 master angler. I'm open to anyone's advice or pointers on past experiences.

I'll update the thread with progress pictures as I get them. I won't be doing the glass work but I will be doing the rigging.

Thanks

[Ironmanangler]

Here's another

[Old'sCool]

Raise the transom to 25" if you're not going with a bracket

[Ironmanangler]

Originally Posted by Old'sCool

Raise the transom to 25" if you're not going with a bracket

Thanks. I plan closing the transom and adding a bracket. Want to power it with Yamaha 200 I4. I'm also thinking of going with a smaller tank then the original. I'm still in the planning phase. Thank you for the input. Keepem coming

[Bigshrimpin]

who trimmed the cap?

[Ironmanangler]

Originally Posted by Bigshrimpin

who trimmed the cap?

Honestly I don't know. Previous owner said he did. His reason was because he wanted to lower the cap height and give it a better look. I'm hoping my glass guy can get things lined up right. Have you seen this done before with other seacrafts? I've seen others raise the floor but haven't seen cut caps.

[Bigshrimpin]

I've seen people raise the caps a few inches, but never lower them on a 20MA.

[Bushwacker]

Originally Posted by Ironmanangler

Thanks. I plan closing the transom and adding a bracket. Want to power it with Yamaha 200 I4. I'm also thinking of going with a smaller tank then the original. I'm still in the planning phase. Thank you for the input. Keepem coming

FYI - Since you're in the planning phase, better plan on moving gas tank, batteries and console as far forward as possible! Don't know if you've read my post on the subject, but a bracket, heavy motor and smaller gas tank on a 20 are all moving in the direction to adversely affecting CG/balance, self bailing capability and ride of the boat! If CG isn't corrected, you can expect a min planing speed in the low 20's. As originally designed and powered, these boats would plane at about 12 mph, which is a big deal if you plan to run offshore in big seas!

[Ironmanangler]

Originally Posted by Bushwacker

FYI - Since you're in the planning phase, better plan on moving gas tank, batteries and console as far forward as possible! Don't know if you've read my post on the subject, but a bracket, heavy motor and smaller gas tank on a 20 are all moving in the direction to adversely affecting CG/balance, self bailing capability and ride of the boat! If CG isn't corrected, you can expect a min planing speed in the low 20's. As originally designed and powered, these boats would plane at about 12 mph, which is a big deal if you plan to run offshore in big seas!

How forward? I plan on going with a 50 Gallon tank, Original console and storing 3 batteries inside the console. I had planned on moving them forward. I was reading your thread just the other day but never finished it. I just don't want to go too forward and affect other performance aspects.

[Bushwacker]

What "other performance aspects" are you concerned about?

About the only performance advantages I can see in a bracket is the claimed 2-3 mph increase in WOT speed in flat water, which comes at the expense of ride and low speed planing capability. You gain WOT speed due to the CG shift caused by moving motor ~30" aft, which raises the bow, reducing wetted surface and drag. My experience is that when you apply the necessary band aids (AV plate fin & 4B prop) to regain low speed planing capability and good ride, you'll lose most of the WOT speed you gained with the bracket! So all the bracket really buys you is a bit more room in the boat AND the safety of a solid transom (which IS a significant improvement if you run offshore very much!)

What you're really asking about is how much should you shift the CG, if any? I would never claim to be smarter than Carl Moesly who designed these boats after decades of boat building, flying and racing experience, so I'd try to keep the CG as close to the design point as possible!

Here's what I'd recommend to calculate an approximate distance to move stuff:
1. Assume the as-designed CG was at the center of the fuel tank. (As a veteran pilot of military transports, Moesly knew how important it was to not change trim as you burn off fuel!)
2. Assume the design motor weight was 300 lbs, on transom, with a single battery at stbd chine just ahead of transom. The design "Motor moment" is (300 lbs) X (distance from transom to center of fuel tank).
3. Use weight of new motor (not the advertized "dry" weight, but "wet" weight including oil & gear lube @ 7.3 lbs/gal, plus weight of the cowling) plus the bracket setback dimension to calculate a new "Motor Moment".
4. The increase of the motor moment, in ft-lbs, is what you'll want to offset by moving batteries, fuel tank, console, etc. so by knowing what all that stuff weighs, you should be able to figure out how far you'll have to move it.

BTW, when looking at these newer "light weight/large displacement" 4-stroke motors, remember that they got most of the weight savings by just removing iron cylinder sleeves! That means that if, for whatever reason (clogged filter, stuck anti-siphon valve, air leak, fuel hose kink), you ever starve the engine for fuel that leans out & overheats a piston and scuffs a cylinder, all it'll take to fix it is a new block! The days of a simple bore & hone plus piston replacement are history for those motors. That's why the modern DI 2-strokes, which achieve even lighter weight, quiet smokeless operation, and low fuel burn without that compromise, are worth a hard look IMHO!