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1
Any reason one cannot fabricate the rear framing from plywood and maybe a layer of biax in the middle?  The best I could do was $80 for two 8í cvg 2x4.   I have enough scrap Iím sure I could make 4 nearly any size and shape I want.
2
Wow. I did one side of the second layer of bottom today.  I thought it was way worse than fitting/gluing the bottom on.  I used 30 minute hardener with a shop temp of 60-65F.  I had plenty of time for both jobs, but I sure wish I had someone to feed fresh epoxy to me. 
  I had the  chance to use Rbobís busted screw removal technique.  I used a soldering gun to preheat the screw, but it wasnít very warm at all and worked well.  It so easy thereís really no reason to leave a broken screw behind.  I used a gasket punch instead of a drill and it makes a perfect hole without making a ugly hole to patch.
3
In the overhead view I was attempting to show the shape of the transom as it leans aft.  It looks like sheet 000d.  I just didnít add anymore detail like you did.  I built the transom per plans with four more inches added to the sole.
  I think I will cut everything off and leave the stringers wild for now.  I can always cut them off if I change my mind later
  I had not planned on any bracket or jack plate is there really any advantage?   I donít even begin to know what the prices are or where to find one.

Ah!  I get the view ... thanks :)

4" to the sole .... keep in mind that in the original design, the lower motor mount bolts are right between the bottom of the drywell and the deck.  If you raise the deck, which is a great idea, just make sure you account for where those lower bolts come through so you can either leave the deck open to the bilge or have access through a large deck plate to those bolts.  And it's a good idea to use an aluminum plate as a big washer for those bolts too.  They'll stay trouble free the longest that way (you should check their torque now and then for the first few trips.

My preference is for a short jack plate.  It'll let you tune the cav plate-to-water height just right.  I like that better than 'move that heavy motor up or down a set of holes' (which usually leads to calling it "good enough" and NOT adjusting it).


Brian

4
In the overhead view I was attempting to show the shape of the transom as it leans aft.  It looks like sheet 000d.  I just didnít add anymore detail like you did.  I built the transom per plans with four more inches added to the sole.
  I think I will cut everything off and leave the stringers wild for now.  I can always cut them off if I change my mind later
  I had not planned on any bracket or jack plate is there really any advantage?   I donít even begin to know what the prices are or where to find one.
5
Todd,

Nice sketch!  Looks like it'll work, but I have one question.  In the top view of the transom, you've got angular sections rather than a flat transom?  If not building a laminated curved transom, then you'll want those nice heavy motor boards (2 LVLs, one above the other) running clear across the boat from one side to the other.  Now, if that's what you are doing and those angular sections are only higher than the motor boards, then that's fine.  Just use strong transom-to-side and transom-to-bottom seams with milled glass fiber, wood powder, silica epoxy mix and strong glass.

Plus, I suspect you'll have a short motor bracket or jack plate between the two swim platforms?  Make sure the manufacturer's clearance requirements are met for when the motor is turned hard to the side.  I expect there's enough room between the extended stringers, but you'll want to verify that.  If you don't know what motor you'll use yet, just check several manufacturers and outboard sizes and design for worst case.

Brian

6
This is kinda what I had in mind. What do you think?
7
Thanks Dan, for sharing!

Now go get that thing wet and post pix of blood on the deck!  :D  All those fish are swimming right past you unmolested and that ain't right!

Brian

8

That curved transom sure is a beaut! 

Brian

9
Nice progress Todd! Almost time to get some sides slapped on that thing. :)

Brian, from your answer to (2) here, as I am also kicking around scarfing some extra length on the bottom panels to max out my stringers, what types of performance or stability issues manifest when the bottom back portion isnít perfectly flat or true? I have seen mention that it should be in numerous places, but havenít heard an explanation of what the adverse effects are if itís not. I imagine it probably depends on the type of defect (cup, curve, etc) but would love to learn more to make a more informed decision.

Ideally, you want water to slide straight backward off the bottom of the boat, disconnecting cleanly at the transom.  This will produce the best efficiency and performance.

As far as what defects do what:

- If the bottom is a hump near the stern, it'll tend to suck the stern deeper into the water (bow higher), and part of your horsepower is going into maintaining that downward suction on the stern of the boat.  Same thing, but much lesser, occurs if the radius of the edge where the transom meets the bottom is too large.  If the issue is too large (hump), you can also introduce porpoising to the boat (same thing as a boat with a CG too far aft due to loading etc).

- If the bottom has a hollow towards the stern, it acts more like trim tabs, pushing the bow down and making it plow a little more than it should ... again, a waste of energy from your motors, lower fuel efficiency.

- If you have both humps and hollows, or one side has a hump and the other a hollow, then you've got situations fighting each other and see more of a general loss of efficiency (which also means speed, BTW).  If one side has a hollow and the other side a hump, then the boat will heel to the side that has the hump when on plane.

You achieve optimal planing trim and fuel efficiency if none of the issues above exist.  That's the goal.  It's easiest to extend bottom length when all plywood is flat on the shop floor.

Something else to consider is that this boat tapers narrower from amidships to the stern, so extending the boat would continue that tapering and it'll appear that the transom is too wide as a result.  The RIGHT thing to do, assuming putting the original transom design at the stern end of the boat (not the swim platform shown above), is to allow the transom to define the width of the stern even if it means moving shelves outward to do so.  This will produce more of a gap between side panels and the chine flats, but it's perfectly fine to fill them and glass the seams right over the filled gap.  It'll be small... a quarter inch or so.

Note that if the hull lengthening or 'extension' is a swim platform behind the transom, that it's OK to allow the small amount of taper to continue, but I still prefer the swim platform being as wide as the original transom, even if it introduces a gap along the edges of forward or 'original' transom... It's all fine tuning though, small gaps, and will work either way.  I just like more flotation in the stern than less...

Does that thoroughly confuse things?  :D


Brian

10
Thanks Jason.  I feel like itís almost about to look like a boat.  It sure is nice to have so much more room in the shop.

  Brian, I have no intention to use a bracket.  It sounds like the sponson idea is not the best choice for my build after all.  I didnít realize until further study that the motor was back as far as the sponsons.  My build will be much different than  the boat we are talking about. 
   I think after you pointed out so many differences Iím going to trim off the the bottom past the transom and mock up the swim platform for you to look At.

Lots of thinking goes into a boat, and it'll be great when it's done!  And yes, definitely post sketches and we'll get it all tuned in before you invest time and cut wood!

Brian
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