Advice on a large project RE hull extension.

[Little Bighorn]

Hi everyone. Great info & great site. Thanks for the read.

I will probably have a few questions posted but one has to start somewhere so here I am. I've read a bit but couldn't find a similar situation hence this post.

I have started a pretty big project about 3 months ago on a F/g hull. Sportfisher kind of boat that is around the 28ft mark. I have taken a perfectly healthy Flying bridge cruiser & cut the deck off, raised the bow & much more to go. I'm enjoying it & wanted to get some well knowledged people aboard to give me good solid advice on propper design as I have too many ideas & loosing confidence on the best way to go..

A breif description so that you get the jist of what the foresight is....
The boat is almost totally stripped & empty except for stringers & bearers or at least will be...so old weight distribution will not apply anymore. I have bought a SINGLE Yanmar 6LY2A-STP Deisel Turbo 440hp to power her as opposed to the twin Chrysler v8's that were in there. The weight comparrison is very minor between the two engine setups. Both being around the 1200lbs approx. Because of this engine I am going to be cutting a minor tunnel in due to the size of the prop being 24inches or more plus a skeg for protection. But this question is about the length extension.

I am wanting to extend the boat by about a foot & a half at the transom...maybe even 2ft!!! I'm trying to gain a little more deck space & visually have it look in proportion with the new top i'm designing. I will also incorporate a marlin board in the mould

Here are my thoughts...Without going through the grind n prep proceedure

Cut "old" transom only "sole height"
Mould up a complete new extension all the way down to "v" (tunnel) & increasing tunnel flare.
Design a new marlin board into the extension
Mould in ressessed trim tab space.
Add stringers inside the extension running in the same position as stringers infront of the old transom.
Strengthen the old half transom & prep for a new sole to be layed.
Foam core new transom & design a door.
Add livebait well into transom wall/gunwhale.
Install single rudder inside the new extension.
Bringing engine further aft to match new rudder position.
All work is with Vinylester resin

Since I have no weight distribution yet, it gives me more scope for making the extension without effecting the ride yet. I dare say that the bow will be heavier than originally anyway so the transom will offset that & keep me in perspective. I also think that I will save alot on weight from old furniture & excess garbage that was used as it was built 30 years ago so new materials will not weigh as much. Plus i can move the engine aound too then (very last job) She used to be right on 4 tonnes (8000lbs). I will be suprised if I gain an extra 2000lbs. Realistically I'd say 9000lbs. Regardless the engine will breeze it in.I also thought that by leaving the original transom half way down in tact would preserve it's structural wholeness & to just build around that.

Amoungst the fact that I am crazy...is there anything that I have not considered or maybe a better way????

Here's a pic of the new look. The line represents the old hull & bow extension. Still at ugly stage but will give you a good idea on hull design.

Cheers & hope to read some cool stuff.

LBh