Bracket vs hull extension vs stretch????

todosier · #1 11-04-2010, 04:43 PM

Hi all,

I have been lurking here a good while and been soaking it in. I have a 20’ Seafari I am planning on starting a full teardown on soon (this was Otto’s 1970 i/o). My goal for the boat is a fishboat for Long Island Sound, not the biggest water, but sloppy water. I would like to have a closed transom and a fair bit of power (a light 140-150 hp). Low planing speed is important.

I understand how flotation brackets fit into the picture on these boats and the pros and cons. The question I have is what would the downsides be of extending the stringers and using the existing stringer system for support of a “bracket-like” extension rather than adding a bracket to a finished transom? If I have to “do” the transom and floor already it seems like the approach of extending the stringers and hull would be less weight in the end. I understand the time/effort/expense in all these approaches vs. adding a bracket. I’m looking for a project.

I can see three ways to go…

The first you could stretch the hull 2’ (or 2.5’) using the structure there and the original full transom would stay to become a false transom. I haven’t seen much talk of stretched 20’s, I know these hulls are long and narrow already. Thoughts?

In the second, you could extend just the hull center 2’ (or 2.5’) using all 4 stringers and hang the motor on the extension (see drawings). The extension could comprise the center and leave room for tabs outside. This would offer less flotation than stretching but more than a bracket since it would be deeper and displace more water (but would not offer the clean water/raised motor benefits of a bracket). Thoughts?

In the third case you could add an extension that duplicates a bracket by extending the stringers, but has a step in the hull as with a bracket (see drawings). This would exactly duplicate a bracket, but would probably weigh less without having the structure of a full transom with a bracket bolted on to it.

Original hull in blue, additions in red.

These may not be original thoughts, but I haven’t seen them discussed. I can see some concerned with the aesthetics of modifying the structure and I appreciate that feeling, but I don’t see a whole lot of difference from bolting and 5200ing a bracket on. I’d also rather see an old girl used and abused than idle.

Thoughts? I’d love to hear them.

Tod

Bigshrimpin · #2 11-04-2010, 06:12 PM

TDosier - It's a LOT more work to build out the transom and extend stringers vs. bolting on a bracket for very little reward. Center of gravity is a bit of an issue with a bracketed 20. One thing that helped me was removing the door and storing 128quart cooler full of ice and fish in the stepdown area. Tabs are an absolute must have with the bracket.

hermco · #3 11-04-2010, 06:29 PM

You can do a hull extension bracket. I recently built a couple for RIBs. Build bracket/hull extension mold, build part with it's own stringers.Bolt on part with 5200 sealant then glass seams. Quick and easy. I have a slideshow on my website homepage that shows the finished products.

I did not do the rest of the rebuild so the boats are still not complete and in the water but the 730 Willard RIB has been water tested with excellent results.

todosier · #4 11-05-2010, 08:37 AM

Quote:

TDosier - It's a LOT more work to build out the transom and extend stringers vs. bolting on a bracket for very little reward. Center of gravity is a bit of an issue with a bracketed 20. One thing that helped me was removing the door and storing 128quart cooler full of ice and fish in the stepdown area. Tabs are an absolute must have with the bracket.

Big,

I know I'm talking a major effort vs buying a bracket, but... have any thoughts on the various options otherwise?

Tod

todosier · #5 11-05-2010, 08:41 AM

Quote:

You can do a hull extension bracket. I recently built a couple for RIBs. Build bracket/hull extension mold, build part with it's own stringers.Bolt on part with 5200 sealant then glass seams. Quick and easy. I have a slideshow on my website homepage that shows the finished products.

I did not do the rest of the rebuild so the boats are still not complete and in the water but the 730 Willard RIB has been water tested with excellent results.

Thanks, I'll look up the slideshow, I hadn't thought of it that way.

Tod

shine · #6 11-05-2010, 11:38 AM

If you extend the hull running surface, you will change the dynamic stability and how the boat planes. Not somethign you want to do unless you are able to calculate and predict the what your new hull will do. Raising the bracket slightly allows the water to break clean off the original planning surface (hull), but its there almost in an instant for displacement when you come off plane or a swell overtakes you.

AS far as making it yourself and tying it into the stringers. I gave this thought myself for my 23CC and I have seen it done before. Its a ton of extra work, but it is possible. I will go with a bracket for my boat, I would rather spend the time and energy on other parts of the boat.

FELLOW-SHIP · #7 11-05-2010, 12:12 PM

Hi todosier

Over the years there has been some talk on this topic and project so fare I have not seen much regarding the actual project itself.

I have always kind of liked the concept but the practicality, the level of difficulty and the time and effort has always cause me to shy away from cutting up my boat as a experiment. I have always been a believer that the second mouse gets the cheese and the first mouse gets his head handed to him.

One of my practicality barriers is WHY would I want to make a 23 SeaCraft out of a 20 SeaCraft WHY not just buy a 23 and be dune with it??

As far a difficulty goes it’s a lot harder to extend a hull that to buy and attach a bracket from HermCo and his Brackets really look Sweet.

And then there is the time and effort. When I did my boat I worked slow but did a good job (for a armature) this would take lots of time and Lots of Beer.

FellowShip

………………………….

Just for the Grins

Official 23’ SF Antique Classic SeaCraft Owner

DonV · #8 11-05-2010, 01:19 PM

Quote:

this would take lots of time and Lots of Beer.

YIKES!!!!!......you seen the price of beer lately??

Bushwacker · #9 11-05-2010, 01:33 PM

Quote:

. . . Raising the bracket slightly allows the water to break clean off the original planning surface (hull), but its there almost in an instant for displacement when you come off plane or a swell overtakes you.

There is also a bit of a performance benefit to the bracket. Since the water want's to rise after it clears the transom, when you move the motor aft you can also raise it, at least one inch per foot of setback. Less lower unit in water = less drag, which translates to a little more top speed. I've seen reports that a bracket can be worth 2-3 mph.

Fr. Frank · #10 11-05-2010, 04:30 PM

Hull lengthening changes the hull rocker, which affect the angle of attack when coming on plane, planing and when falling off plane. With the VDH hull I would think you would positively have to have a pad or flat planing surface extended on the keel to enhance longitudinal stability, and lessen wetted surface drag. The alternative would be calculating hull rocker and building that into your extension.