1975 18' sf

[fishfullthinking]

Dave,

I am sure it will be a great boat when you are done. I will keep an eye for your sea hunt, Last week and I went out of Boynton and we got a big king close to 50lb. Looks like they added some rock piles to prevent erosion and there is plenty of bait on those rocks. Keep posting your progress.





Gene

[Tashmoo2]

Dave,

My 1st Seacraft was 23 ft and we fished it up to 50 miles off shore. The 18 ft boat has that same Seacraft feel in a head and following sea. I am really impressed with it, especially when you consider when it was designed.

Thank you for the dimensiions.

Ed

[dginge]

Dave

I'm enamoured by your project. I own a 77 sf 18ft
Let me ask you, is there any wood in the stringers at all or just foam filled glassed in boxes? I know that the floor is wood sandwiched fiberglass and I learned the keelson Is wood cored. Thank you.
David

[dave s]

No wood in the foam filled stringers; only wood I found below decks, is the Kelson and some small pieces where the through hulls were.
The stringers were a well thought out design, considering it was over 40 years ago, when most boat builders put in wood and set it on it's edge.

I fished on the 18' SeaHunt offshore yesterday, and comparing it to the open layout on the SeaCraft, I will have a lot more room on deck.
And hopefully ride better in the slop too.

I've only ridden in my buddy's renovated 20' SF a few times, and it was highly modified with a fiberglass bracket and 150 Etec.
I remember it rode and fished well but was very wet; we fished in some sporty seas with that little boat.
I would have bought it but they raised the deck and cut the shearline, so there was little freeboard. And he had numerous major problems with the Etec.

[dave s]

Transom is cutout.
Used a high speed disc cutter to get the slot started and Sawzall to cut through.
Came out clean and I didn't butcher the hull!
Now that the transom is out, have to add some 2x4s to hold the hull sides in.

What to do next- traditional 25" cutout transom or continue with the hull extension?
The extension is a lot more complicated, esp. to design a mold.

Laid the core back in at 5 degrees instead of the original 12 degrees to see how the bulkhead will look.
Prefer a more vertical bulkhead for more toe room and not to lean out when braced in the back.
Also this allows me to make the transom cap narrower.

Back to Home Depot tomorrow to look for mold supplies.

[Bushwacker]

Originally Posted by dave s

. . .
Laid the core back in at 5 degrees instead of the original 12 degrees to see how the bulkhead will look.
Prefer a more vertical bulkhead for more toe room and not to lean out when braced in the back.
Also this allows me to make the transom cap narrower. . . .

If you're hanging motor on transom, that shouldn't be a problem. However if you decide to install a bracket, just be aware that it will have to be a custom job, as most brackets are not built for the oddball 5 degree angle!

[dave s]

Thanks Bushwacker!
The 5 degrees is only for the bulkhead; if I make a bracket, where the motor mounts will stay at 12 degrees.

I read your post on Brackets-pro and con. And every other thread!
After owning and fishing a few cutout 25" transom boats. I would really feel safer with the full transom.
Since I'm redoing the whole boat anyway, I can move a lot of weight forward.

Do you think a hull extension will help with the Cog balance at speed, compared to a regular bracket, where the tub is raised up a few inches?

I'm thinking besides the static flotation, the extension will help lift the rear a bit while running.

I'm not so concerned with top speed, since most days I'm running in 2-3' chop.
So So the supposed speed benefit of the raised tub, isn't as much a factor for me.

[Bushwacker]

Originally Posted by dave s

Thanks Bushwacker!
The 5 degrees is only for the bulkhead; if I make a bracket, where the motor mounts will stay at 12 degrees.

Ah, that makes sense - thought it was strange that what I thought was transom core was so far forward of aft end of hull!

Originally Posted by dave s

. . . After owning and fishing a few cutout 25" transom boats. I would really feel safer with the full transom . . .

Amen brother! After making one return trip from the Bahamas in 6-8' following seas in my boat with a 20" transom cutout, I can relate to that!

Originally Posted by dave s

Since I'm redoing the whole boat anyway, I can move a lot of weight forward.

Do you think a hull extension will help with the Cog balance at speed, compared to a regular bracket, where the tub is raised up a few inches?

I'm thinking besides the static flotation, the extension will help lift the rear a bit while running.

I'm not so concerned with top speed, since most days I'm running in 2-3' chop.
So So the supposed speed benefit of the raised tub, isn't as much a factor for me.

Moving weight forward to maintain CG is the key to good performance with a bracket, especially on a smaller boat.

Regarding a hull extension, Carl Moesly's comment, when I asked him what he thought about the bracket on my boat, was "Why not just make the hull longer?!" So yes, a hull extension will not shift the CG like a bracket will. It will provide most of the benefits (except for WOT speed increase) of a bracket with none of the negative effects, so it's the best although most difficult/expensive option. Even with a maximum flotation bracket like a Hermco, the flotation tub will be out of the water when you're on plane, so that flotation goes away, causing a significant aft shift in CG.

Suggest you send a PM to Blue Heron, as he's thinking of making a hull extension for a 20 I/O CC model he bought a few months ago. He found a technical paper and some software from some folks at Stevens Institute, where they modeled and tested deep V hulls comparing baseline, bracketed, and extended hull configurations. The model predicted and hydrodynamic testing confirmed that the bracketed model runs with a higher trim angle (bow higher out of the water) and has a higher minimum planing speed than either the baseline or extended hull models. This explains the higher WOT speed for bracketed models, but it also implies a harder ride because the sharper sections of the V are not in the water at cruising speed. This theory and test data match my own experience, and is why I've been preaching in this post that, on a 20, you really need to avoid using a heavy 4-stroke motor on a bracket! Potter's arguments in favor of a bracket regarding safety and WOT speed/economy are correct AS FAR AS THEY GO, BUT THEY DON'T TELL THE WHOLE STORY! If you can't shift weight to maintain CG location with a bracket, I believe the modifications you will have to make to an get acceptably low min planing speed and soft ride at cruising speed will reduce prop efficiency and increase drag enough that you'd get BETTER CRUISE performance with the motor mounted on the transom!

I could not shift weight on my Seafari without making unacceptable mods to the boat, so even my DI 2-stroke motor is too heavy for use on a bracket. I had to add some band aids like a stern lifting 4B prop and a Doelfin to get my min planing speed and ride back to what it was with a 300 lb motor mounted on the transom. The 4B prop really helps you hang on plane down to 12 mph, but it has more blade drag so gets lower MPG and WOT speed than a good 3B prop. The Doelfin also produces lots of stern lift, but at the cost of extra drag, and my tests with the I-Command system, which calculates instantaneous MPG from a GPS spedo and fuel flow from engine computer, indicate that it costs me 0.1-0.2 mpg at cruise. I left it off for my recent 90 mile trip up to the Long Point gathering for that reason, since most of the trip was in the ICW where I didn't have to slow down to 12-15 mph to punch thru 2-3' square waves like I've often had to do on the Little Bahama Bank!

The bottom line is the benefits of the solid transom, big swim platform for diving, and extra room/storage in the boat provided by the bracket are big enough to me to justify a slight reduction in cruise performance, so I'd do it again, although I might consider using the ~50 lb lighter 125 hp "115" E-TEC that wasn't in production when I bought the 150. Optimum cruise on the 165 hp "150" is only about 35% throttle and it only needs 45% to climb on plane, so I'm convinced the "115" would still have adequate power but would burn about 30% less gas. However I've consistently averaged 4.4 mpg with the "150" on trips of 200-700 miles with heavy cruising loads, so I can't really squawk too much about fuel burn with the current configuration, considering that it has so much margin for even heavier loads if necessary!

[dave s]

Thanks for the reply!
That's why I think the hull extension is the best solution for me; just a lot more complicated.
I have limited space and equipment, so I need to make it with simple methods and tools.

I can make it in stages, such as making a simple, one piece transom first and then cutout the opening for the tub. But I'd have to glass the tub later- wet on dry.
To make it wet on wet, I'll have to make a more complicated mold, so I can do the layup at one time.

Right now I'm leaning towards making a one piece mold, about half the transom height, basically from the tub level down. It'll be more like a Euro Transom, where everything will be tied together.
Even the deck could be the integrated into the tub by extending it into the swim platform, if the heights work out.

Then I can make the bulkhead later, at whatever angle I want.
I could glass the bulkhead into the deck and sides, or make the bulkhead with an opening like a door or even wider, have the whole thing fold down, like a gate.

Some interesting possibilities!

Got some 1/2" MDF board and 1/4" Melamine panels, and 2x4s today, so after some grinding, I'll start playing with the layout.

Would be nice to cut some Formica faced 3/4" board and build a frame to hold the extension in place, but since I don't have a miter saw, I have to make the cuts by hand. The MDF board also doesn't have a smooth coating, so thinking of coating the mold insides with epoxy and then wax or wrapping the parts with packing tape.
Glassing is going to be the easy part.

[dave s]

My latest thoughts are to make an Euro transom, like on a 21 Contender.
I won't have to make a hull extension and can use the original transom line.

With the bulkhead set about 0 degrees and 12" ahead of the transom, I'll get a small swim platform, and actually have more room than the original 12 degree transom and cap.

I'll have to make a gate, so the motor can pivot all the way up, but this will make it easier to get to the swim platform or make a door, so I can slide big fish in.

With all the other modifications I've made, I will still have a lot more room overall.

With a traditional cutout transom, you need a wider cap, and a splashwell to keep the water out.
I could just make it a 25" cutout, but I've owned/ fished open transom boats, and don't like the water coming in.

So with the Euro transom, it'll keep the water out and it's simpler to make.

The amount of room I'll gain with the extension may not be worth all the work.

Any thoughts?