20' SeaCraft heavy motor
 

So I have read just about everything on these boats. I am in the middle of restoring a 1969 20'. I am planning on a Hermco Bracket. And I will be putting my fuel tank as far forward as I realistically can. I am also making it a flush deck all the way forward and it'll be raised 3 inches from factory.

I am not sold on any one motor yet. But am leaning towards the 200 Suzuki. It is heavy but I have seen them with heavy motors before. The 250 Pro Xs is slightly heavier, how would it run with a 250? I've seen 250s on some 20's.

Could the boat perform well with the weight? I am moving the tank, and console forward. Or am I just crazy?

Hummmm.......run with a 250 Pro XS???, how does "like a scalded ape" sound. NoBones has a 200 Merc 2.6L (I think a 2.6) and it's fast, real fast!! Why not a 150 Pro XS?

Or am I just crazy? :)

If I'm not mistaken, No Bones motor weighs about 405 lbs.
Asset's choices are closer to 500 lbs. Light is right on these hulls. Latest thread re. the 20 with extra power/weight below:

http://www.classicseacraft.com/commu...ad.php?t=28260

Good luck with your decision and don't forget the drag chute and ride safety waivers:D

These boats do not perform well with a heavier higher horse power motor, they are not speed boats, a 150 is the max you should put on it you don't want it chine walking.

No, I keep telling you, I`m crazy.
You are just a cheap bastard and I am an antique slacker.

Bones has some port action going on and dyno`d 238 at the prop...
He sees 62-3 light and she will chine walk.
He also has no liner and no bracket so weight and balance are right on the money.
No bracket either to screw up the CG.

The real kicker is the massive 12x 24 tabs.
The only things in the water are the prop, pad, and tabs at speed.
Dave has the ultimate tabs on his 25 Seafari.

Now Sandy, I'm only a cheap bastard because I'm a poor bastard!!!!! However NO argument on you and the crazy thing! :)

I do know there was no way, I mean no way I could even keep Ken in my vision after about five minutes at WOT at the Sebastian gathering a few years ago. I was doing what I thought was pretty good speed in the old clunker trying to keep up with him and he was just a dot getting smaller and smaller off in the distance.

Move everything forward get 5 fat buddies strap them in on the front and hang this on the back

Hold on

Well I think I'll be leaning towards a 175 pro xs. This should give me some good all around performance. My question is, how far forward do I have to put the tank? I'm planning on around a 60-70 gallon tank. And I want the boat to sit level in the water or close to it. I also have a very small console out of an 18 seacraft and I plan on having the batteries and possibly oil tank in it

I have a 225efi merc weighing in at 475lbs, no bracket and it performs nicely, and boat self bails with no problem

Estimating CG Shift- Offshore Asset & mike c
 

Offshore Asset & mike c-

You both asked similar questions with respect to engine weight & moving things around to compensate. With all the discussions about heavy 4 strokes particularly on brackets, I put together a quick tool to use as an estimator. See my post, Capt Terry, of 9-24-16 on Estimating CG Shift with Heavy Engines. Be sure to open the attachment for an example calculation. This puts a little science to the quesswork. Also see Bushwacker's related post of 9-25-16, as well as some others. If the tool helps you, great; if you don't like it you will have wasted little time. Good luck.

I had the exact same motor set up as Jwclbi on a 20' Sceptre no Bracket but on a 4" setback jack plate... Loved that boat should have never sold it. Ran like a Scalded ape, Handled Great and Kick Ass fuel Economy...

That 175 pro xs puts down about 190 hp at the wheel.... U can run anything up to a 250 IMHO without issue... My EFI weighed in at 475 lbs and put down 245hp at the wheel...

Hang the power on you won't be dissappointed.

Just my 22 Cents
Robert

Hey there Gameon do you remember what your boats speed was at full throttle?

I ran a 1991 Mercury XR4 2.4L on the back of my old '72 Seafari. Originally 175hp, after rebuild it produced about 210 hp. I had a Bob's nose cone on a lower unit from a 225 Merc, low water-pickup, and ran the motor fairly high on the transom, turning a one-of-a-kind custom 3 blade prop from Power Tech, 15x16.5P

My maximum speed (with everything just right) was 53 mph at 6050 rpms. But everything had to be perfect to get that speed: minimum weight and minimum windage, air temp below 50*, low humidity, running into an 8-10 mph wind, moderate chop to get more hull out of the water, etcetera.

Most of the time I couldn't get over about 47-48 even with the higher hp. And I normally never ran over my 25-26 mph cruising speed because of fuel consumption with a 29 gallon tank.

So I repowered with a 90 Optimax, and went from less than 2 mpg, to nearly 7 mpg average. I loved it.

In 1969, the largest Mercury outboard was 125hp and it weighed 270lbs. The 20 seacraft hull was NOT designed for heavy modern power. You have to slow down to a 18 - 22mph cruise when the waves hit 2ft. When it's flat calm, the top speed for the hull is in the 50's before it starts to walk. Check out a merc 115 4 stroke or something under 400lbs.

Just looking over the 1974 pricelist. If weight was an issue, why were the 20's offered with so many different v8 sterndrive options? Those small blocks must be close to 7-800 lbs with the drive and steering.

Marketing?

Why indeed.

A good portion of the I/O is forward of the transom.

Think teeter totter.

CG is much more important than weight, ie., it's all about where the weight is located. Carl Moesly told me that the CG on an I/O Seafari with the 4 cyl MC is further forward than it is on the OB version with a 300 lb motor on the transom! I think those V-8 I/O's are closer to 900 lbs, but the CG would probably still be further forward than it'd be with a 500 lb 4-stroke hanging on the transom!

Could be.
Could be.

He understands much more than most of "We".

Vortec with 71C is 900lbs, with an I/O probably over 1000.

I used to see a gal and her young squids in a 4 cyl version. For a bit.
And then they would pull away into the sun.

I guess I need to get me some Lencos.

I think you meant to say Bennett's. :)

Maybe the only thing that won`t break.

How true Sandy!! I had Lencos on my 22 Pathfinder, the best thing about them was the actuators were easy to replace, a couple of screws, splice the wires and prepare for the next replacement. I would buy two when I found a good deal, nice to have a spare at home. Plus the old ones looked right at home in the garbage can.

So after giving it some thought. I think I might be skipping the bracket and going for a traditional motor on transom approach. I don't want to pour as much money into it as I originally thought. And I scored a sweet $1,000 Aquasport 17 with a 1998 Johnson 115 that I plan on using until I finish the seacraft. Then running that 115 on the Seacraft until I put on a new motor. Luckily the Johnson is really clean and it is a 25" shaft, plus it weighs around 350lbs. I have the transom done. It just needs the stringers finished and a floor.

Offshore, Here is what I think you will see with the correct prop -
Miminum planing speed: 12-15 MPH
Max. Speed: (no tee top, light load) 32-34 mph
Max. Speed: Tee top, 6 tanks, dive gear etc.) 28-30 mph
Fuel burn: 6 GPH @ 4,000 rpm = 22-24 MPH (4 MPG)
Miami to Bimini - 15-18 gallons.
You will not have a race boat, however that is the weight motor the 20' SeaCrafts were originally designed for
- so just sit back a R-E-L-A-X.

Check with Fr. Frank, Tiny, Capt Terry, Denny, Tom Paris and others to see what they think. End to end that crew would have surpassed Magellan's circumnavigation with their 115 HP powered SeaCrafts. Lots of data with them to "adjust" my preliminary input.

That's a good choice and great match for the boat . . . those old V-4's are tough simple motors; ran an old cross-flow (1975 vintage) on my boat for 31 years and it NEVER left me stranded the whole time I had it. Just make sure it rev's about 5500 @ WOT; a 13 3/4 x 15 SST prop worked good for me. I put about 2000 miles on it on a bunch of trips to the Abacos. Used to carry about 65-80 gallons of gas, and a couple of weeks worth of groceries. With a big load in cabin and light motor, I could plane at about 12 mph and ride through a 2-3' chop sitting down! Cruised at about 20 kts (22-23 mph) @ 4500 for hours on end at about 8 gph. Seemed to consistently average about 2.8 mpg carrying heavy loads. Your motor is a looper, so should put out a little more power and be more efficient. (They were rated at powerhead instead of prop in 1975!)

I dont know what pitch prop I have, but my 20' CC with a FICHT 115 will do 28-32 MPH with 3 adults and 30 gallons of gas in the tank.

not sure of my fuel burn, but I can play for a couple of hours in the bay around the St Marks river and only burn 5-6 gallons of fuel.

I cant wait to repower with a E-tec 115!

The boat will be mainly used in Miami and the Keys just running around and live baiting the edge. As much as I love speed, this may not be the boat to do it in. I'll build it as light as I can so I really maximize performance. I already built the transom out of Coosa, and I cut out the liner and will probably run nida-core for the floor while still raising it 3 inches. I also want to build a shroud for the motor. And I have a small console out of an 80s 18 Seacraft. Half the fun is planning it after all

The inner liner is there for a reason . . . it adds a lot of torsional stiffness to the hull, which a CC needs, since it doesn't have a cabin top or full height bulkhead to tie the hull sides together! A lot of guys install balsa or foam core against the hull sides to stiffen up the hull when they remove the liner. Adding some bulkheads under the raised deck will also add some torsional stiffness.

I agree there. The hull is very thin. Could I get away without a coring material and doing a layer or two of 1708? I am thinking that with the bulkheads I put in under the deck, and a big front bulkhead for the anchor locker, it should be pretty stiff. The floor will be going directly to the hull sides as well as maybe 2 vertical supports on each side. I've seen balsa used as coring. Just uneasy about putting wood back into the boat after I took out so much of it that rotted. Any other suggestions on foam coring materials for the hull sides? Is divinycell the standard nowadays?

Carl Moesly built his boats very much like the airplanes he flew for about 25 years . . . light, but very strong! The problem with trying to increase the stiffness of a panel with only a layer or two of cloth is that stiffness of a panel is proportional to the thickness of the panel CUBED! A layer of 1708 is about 1/16" thick. So if you compare 2 layers of 1708 to
one layer of 1/4" balsa core with a layer of 1708 over it, the balsa core will be 27 times stiffer than than the 2 layers of glass, and probably not much heavier! A little bit goes a LONG way when you start increasing core thickness!

The bulkhead in the anchor locker will only stiffen the front 18" or so of the boat, and it's already fairly stiff up there due to the flare in the bow and wide deck, so that won't do much. As far as core materials, end grain balsa core actually has 10X more shear strength and better compression strength than most all of the foam materials out there, plus it absorbs resin very well so it bonds better than most foams. It's good stuff as long as you don't drill holes in it. I've read a number of Dave Pascoe's articles who is a very knowledgable surveyor who has done a lot of research on core materials. Although he's a big fan of balsa, he also likes core-cell, which is one of the newer materials.

One thing about adding bulkheads is that you have to be careful not to create hard spots in the hull. My neighbor is a professional yacht builder and composites expert, and he says the best way is to use a foam fillet shaped like a trapazoid between the bulkhead and the hull. Then when you glass over it, it will create a gradual transition between the relatively flexible hull and the much stiffer bulkhead.

I'm glad I am asking these questions here. A lot of great information. I think I may end up going with the balsa. I do not think I will ever be drilling into it. I'll leave the last foot or so bare for all my thru-hulls and with the inner transom wall tying into the side of the boat, It will be plenty stiff.

My fear is making the boat too stiff. I am sure there is a fine line there. And with weight as well. Originally I was planning on having the tank very far forward, but now without the bracket and heavy motor, if the tank is too far forward it may cause the boat to sit bow heavy. So my question is where do I put the tank? I am thinking midship somewhere and about 50-60 gallons or so.

That should do it for questions as of now

There are solutions for avoiding balsa rot around drilled holes that have been posted on CSC before or maybe Bushwacker can provide a link or better details. As for location of the tank you might be interested in seeing my post of 9-24-16 on Estimating CG Shift with Heavy Engines. Puts some science to it.

Awesome. I put it into excel and I am playing around with it now. I bought the boat as just a bare hull so I do not have anything to work off of. But I think if i just have a 350lb motor (50lb heavier than what you used in the original CG calculation) and I move the batteries into the console, I should be around where I need to be