LOL.....This is true!! Maybe add in an additional 5 hours for my dads time. He just likes to get out and piddle with me on occasion.


Strick,

Didnt you rebuild a yellow 20' Seacraft??? I have been searching ClassicSeacraft high and low trying to find that build thread for that boat for ideas......

Um. It's a sticky. The first thread on the Repairs and Mods forum. "Here we go again"

Oh wow!!! How in the hell did I miss that???? Thanks for the info.

Slowly pecking away at it.... Cut open the box stringers and removed all of the old foam. Also removed the fuel tank and the floor piece that the fuel tank sat on. I'm curious to know who had fiberglassed that piece in as it was 1/4" ply that had one layer of glass on the top side. The underside was raw rotten wood.

http://i1235.photobucket.com/albums/...1/image-55.jpg

http://i1235.photobucket.com/albums/...1/image-56.jpg

looking good!!!, your way ahead of Me on your 20 as far as progress on the tear down go's , mine looks to be in the same shape as yours,totally rotten, I did get my aft deck n splashwell cut out and the rotten transom wood dug out yesterday.

I've cut open a few of them and that's how they came from the factory. Top side of the wood was glassed but the underside was not. I still think your boat is factory judging from the amount transom rot, placement of "Potter Putty" on the stringers and the looks of the foam etc... I would not put it past the factory to use 2x4's imbedded in the foam along the perimeter for extra support.... BUT I've been wrong before :)

strick

Strick.... I think you are right. All factory. And yes, there were 2x4s embedded into the perimeter of the boat down into the foam. There were wood screws screwed inside those perimeter pieces also.

Strick..... I was originally thinking that I was wanting to use Coosa for the transom and Divinycell for the floors, but after combing through your 20' build thread, I'm thinking about going back original with marine grade plywood.

Your thoughts??

I would say if you got plenty of money and are worried about weight on the boat I would go with the composites you spoke of, but if your not worried about weight much and just want it to last till you part with us here in this life the wood is fine. I have saw strick say it before up here "wood is not the enemy" if done correctly the wood will last 30+ years easy. I am using wood in most of my projects and feel like it will out last me and I am a young fellow. On the race boat I will use composites, carbon fiber, coosa, and such but weight will be a big factor on that. One other thing that comes to mind is the resale value. If you are building it to sale composites help sell a boat, but to keep for yourself wood would be my choice. I also think sometimes a heavy boat will ride better and if you get a boat too light it will loose the ride quality but gain some fuel economy. The trick is to get a good over all balance. If your going with a large heavy four stroke stroke on the back you might want the coosa in the rear to help offset the motor weight. I used foam composite core on my bracket build for my 20' because of the 465lb motor on the rear not for the rot free advantage but to try and offset the motor weight for balancing issues.

About 20 hours into the tear down at the moment from the time I started messing with the boat.

Secured the top cap to be removed off the boat..
http://i1235.photobucket.com/albums/...1/image-57.jpg

Top cap removed..
http://i1235.photobucket.com/albums/...1/image-58.jpg

Removed forward fish boxes....
http://i1235.photobucket.com/albums/...1/image-59.jpg

Boat is officially STRIPPED!!! Now it's time to start building her back up!!
http://i1235.photobucket.com/albums/...1/image-60.jpg

Built a roll around dolly for underneath the boat. Now I can move my boat in and out of the shop.
http://i1235.photobucket.com/albums/...1/image-61.jpg

Sitting up on the dolly real nice and stabile. Threw the oversized 23' Seacraft console in it to see how it's going to look.

http://i1235.photobucket.com/albums/...1/image-62.jpg

You may find that there isn't room for vertical rod holders on at least one side of the console, otherwise it might be tough to squeeze by. I have a master angler with a slightly wider cap, and I had to remove the rod holders on the starboard side. If I ever unbolt the console, I will move it to the port side. An asymmetric look, but more practical for me. It might be a little bit easier on a regular Sport Fisherman.

very cool idea !!

There will be plenty of room on either side of this console because I am taking about 8" out of the middle of it to narrow it up. The dimensions on this console will be 49"L x 31" W x 44"H, similar to a console that Birdsall Marine makes. I like this console for the upward height it is compared to the console that came out if it.

When I am done, this console will be even more narrow than the one that came out of it.

I have been looking around online at older model 20' Seacraft particularly the ones with the inboard/outboard set-up. I have been looking at these particular engines that have been put into these boats and they appear to be Mercruiser 135 hp inboards with the Bravo outdrives. The reason I have been looking at these set-ups is due to the weight of these particular engines.

I see all over this forum about keeping the engine as light as possible to balance out the boat and yet these inboard/outboard engine set-ups are WAY heavier than a single outboard engine.

If I am looking correctly, these inboard engines are weighing in at 700-1000 lbs, then add another 150 lbs for the outdrive????

If this is the case, I am thinking about maybe trying to put a Yamaha F300 on my 20' Seacraft. I dont see why it cant be done since I have seen the new F200 on the back of one and the F300 is only 73lbs heavier at 562 lbs.....which is also WAY lighter than those inboard/outboard set-ups.

Again, I dont know why it cant be done since there are many other boat manufacturers out there that are building same size footage boats (bay boats) and sticking larger engines on them with no problems.

I'd like to hear others comments on this........

You're ignoring a key factor in the CG equation! It's not only the absolute weight that's important, it's WHERE it's located, that determines the boat's CG location! The weight of that 4 cyl engine (I think your I/O weight numbers are about right) is probably centered at least 12-18" forward of the transom, while the weight of an outboard will be centered 6-12" AFT of the transom!

I specifically asked Carl Moesly how the overall CG location compared on the I/O's vs. the outboards on the 20' Seafari. He said the CG is further forward on the I/O's, and this is in comparison to the outboard he designed the 19/20' hulls for, the I-6 Merc, which weighed less than 300 lbs! So how does that CG difference affect the performance of the boat? Here's a couple of examples:

CSC member Tiny had an I/O Seafari and sold it after he bought Fr. Frank's OB Seafari with the 90 hp Optimax, which weighs 375 lbs. He said the I/O model rode noticeably flatter and softer than the OB model; I went for a ride in the I/O boat and confirmed that it planed at 12 mph WITHOUT trim tabs! My Seafari would do that with a 300 lb outboard and WITH trim tabs. When I installed a 30" bracket with a 427 lb motor on it, my min planing speed jumped to the low 20's! This was totally unacceptable for offshore use because the 20' hull is relatively light and starts to go airborne over 20 mph in seas of about 3'! In those conditions, you can't even use 150 hp, let alone 200 or 300! I had to add a Doelfin and 4B prop, both of which reduce top speed, to get my min planing speed back down to 12 mph!

Also you should know that those quoted 4 stroke weights are DRY weight! Once you put a couple gallons of oil the crankcase, lower unit and tilt/trim system, I'm pretty sure that F300 will weigh over 600 lbs! The motor weight issue on the 20' hull has been discussed many times on here, and the consensus of the experienced guys is that it's a very efficient hull designed for lightweight motors, so lighter is better especially for a good ride, and around 400 lbs is about the heaviest you want to go for best all around performance! The Seafari has more weight forward so can handle a heavy motor better than the CC's, but you can compensate, up to a point, by moving the console, gas tank and batteries forward to help balance a heavy motor.

And your boat touches 50 light.

I am merely funning about the Yamaha F300.......would be cool and I know it CAN be done as there was just a Mercury 275hp.....but where or not it would be the ideal set-up is clearly another issue.



So does anyone have the center of gravity numbers for a 20' Seacraft Center Console??? I have been reading up a good bit on center of gravity on boat building. To my understanding most boat center of gravity is about 60-65% of the total length of the boat from the bow.

If that is the case, then that would put the center of gravity for the boat at 11.7-12.7" measuring from the bow of the boat back. And this is just with the hull only.

If we were to add a bracket, I was wondering if you had to figure the bracket length into the total length of the boat......going from 19' 6" to 21' 6" if we were to add a 24" setback bracket???? This would move the center of gravity for the boat back 1-2" to 13-14' measuring from the bow of the boat.

I may be totally WAY off on all of this.......that is why I am asking as maybe someone else ACTUALLY knows the answer.

When building my boat back, I am wanting to make sure that I am keeping the boat as balanced as possibly and not just going off guestimations.

I know if I can calculate the center of gravity for the boat I can then apply foot pounds of downward force applied to the boat with however my boat is going to be set-up and optimize the center of gravity of the boat on weight distribution.

ive got a 200 merc just over 400 pounds I have 4 batteries in the console at reast the scuppers are dry till I walk to the very back but for the most part only the channel is wet


http://i782.photobucket.com/albums/y...t/photo-90.jpg

Good. :eek: You scared me.

I believe the CG of planing hulls is normally measured from the transom heel (the point where the keel intersects the transom). It is usually measured as a percentage of static wetted length.

The static wetted length of a 20' Seacraft is about 17.5'. I've been told that a typical CG should be at about 33% of static wetted length, which would put the 20' Seacraft CG about 5'-9" forward of the transom heel. This is not gospel, just some preliminary calcs I've done preparing for my own 20' resto.
Dave

This is the most important question to consider when you add a bracket. The bracket shifts weight and buoyancy aft, but once you're on plane, the typical bracket doesn't produce hydrodynamic lift. So it helps keep the scuppers above the water at the dock, but once you're on plane, it forces the hull's center of lift aft which hurts low speed performance.

I think you're on the right track. Determine the correct location for the CG. Don't figure the bracket into wetted length, and use a moment equation to calculate the effect of engine, batteries, console, crew, etc. on CG.

Dave

Carl said the cg was determined by the tank placement with different thoughts and ballast tank design. If you place the tank just a tad forward of the cg, you may find happiness.

I`m not allowed to ride wheels.

Cheers,
GFS

Being a pilot, Moesly understood the importance of CG location and it's effect on performance better than most folks. He generally installed the fuel tank right on the boat's CG (at least he did on my Seafari), so the boat's trim wouldn't change as you burn off fuel. If you assume that the boat's original CG (with a 300 lb motor) was about where the center of the fuel tank was, I think you would be in the ball park, at least for a starting point.

He built a flying wing hull. How cool is that thought?

So I took the schematic on the SF20 off the specifications page from the front page and printed it out and graphed it. If it is true that Mr. Mosely put the fuel tank right on the center of gravity of the boat, then that rings true with what I was saying previous. The center of gravity on the 20' Seacraft SF is exactly 63% of the total length of the boat. That puts the center of gravity for the boat at 12' 4" from the bow of the boat. In all my readings for boat building, it was noted that most boats' center of gravity was somewhere between 60-65% of the total length of the vessel. This obvious rings true here as well.

Now I am going to try to apply foot lbs of downward force with regards to his layout of the hull along with the max recommended horsepower engine weight during that time this vessel was made and use that info to see what the weight ratios were and try to extrapolate that info to how I want to rig the vessel today.

Taking into account 4 stroke weight?

I will be looking at max hp 2 stroke weight that was originally recommended for the boat.

Once you find the center of gravity of a boat, you are supposed to be able to measure out foot lbs of weight of downward force on the boat as the weight moves away from the center if gravity of the boat. I plan on trying to figure out the most weighty objects in the boat and try to see what the weight distribution looks like.

Taking that info, I will then mock the weights of the new engine I am wanting to use and how I want to set my boat up and see what my weight distribution would look like and see how it relates to the original design set up. I can then move weight around in the boat to try to get as close as I can to what the weight distribution design was originally.

If you look at the two different spec sheets... One on the SF 20 and one on the Seafari 20, you will notice that the fuel tank is in two different spots. I don't believe this is due to the center of gravity changing because the center of gravity of the hull shouldn't change. The SF20 has a more open bow and is lighter in the front end so the fuel tank appears to be positioned near center of the boat. The Seafari 20 on the other hand has a more heavier front end due to the cabin and thus if you see to where the fuel tank is located it is located more off center towards the stern of the boat. Also of note was the use of a more lighter capacity fuel tank at 38 gallons. Again, I do not believe the center of gravity of these boats change.... Rather it's more of a changing of weight distribution around the center of gravity.

The boat in this video has the new f225 which should be the same weight as the f300. You might be able to get in touch with whoever did this restore to find more info on what they did to offset the weight if anything.
http://vimeo.com/67663992

Not affiliated, just happen to stumble across this video the other day.

That's what I'm talking about!!! I see too many Key West bay boats in my area with Yamaha F250's on them and they are not much larger than the Seacraft. I really see no reason as to why an F300 couldn't be ran on one.

I may have to give Tuuci a call and see if they would be will to give me the contact info for the owner if that boat.

Thanks a bunch!!!

If they don't, I bet caymanboy may know him.

OMG !... This is why I hate coming on to this site. SO much want in all these threads. Makes me miss my 20 so bad. Why o why did i ever let her go =*(..... Nice work so fare buddy keep it up.

Here is an 18 I just built and installed a Bob's 12 inch Jackplate on. Probably going with a 14 inch on the 19 redo.

Yea, I am thinking about using a shorter extension bracket and then using one of Bob's 6" jackplates. Would give me around 18" set-back instead of 24" if I can have a bracket made that size.

Somebody down there in Mijami loves their SC 20 SF's.

Personally the CG on that boat doesn't look right to me. Engine is trimmed down all the way, boat is still proposing.
Anyway, speed on these boats is like golf, pretty easy to get 110 par, or 50 kts, everything after that takes a shitload of work.
You can throw all the HP and (weight) you want on the back, everything over a 200hp 2 stk is gonna be tough to get MPH.
Once you throw a bracket on the back, bigger tank, bigger engine, it throws the CG off, no matter where you think it is.
Just sayin. :)
Annnd, if you where gonna put an F225 on a boat, why not a F300? Besides Insurance. :)
Anyway, nice rig, not overly fond of TUUCI's new "Shadeblade" design, looks tippy. :)
On mine, I can undo the straps and fish.