Question on re-lofting my TNT

Questions about modifying a design

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DSR
Posts: 270
Joined: Mon Mar 21, 2016 8:11 pm
Location: Allegan, Michigan

Question on re-lofting my TNT

Post by DSR » Thu Sep 29, 2016 3:31 am

Hi everyone
I have this post on my build thread but i figured it would be better if i tossed it on here as a new topic as it seems to be a more appropriate spot:

Did some more extensive measuring on the Honda and it looks like I'll be doing a bit more modifying than I originally thought.
The original 11' design shows spacing from frame 3 to the transom as 32"/32"/29" and it looks like I'll be stretching the hull out to 12' 6" and respacing the frames and transom to 37"/37"/37" to fit the powertrain behind frame 1 with the drive extension.
Not a big issue as far as I see it. I was going to loft the boat out anyway just to learn how to do it, but now with frame 1 being "out of proportion" with the rest of the frames and changing the transom angle to 90° it turns the dimensions for frame 1 into a bit of puzzle to reverse-engineer to re-fair the hull lines.
I've wrapped my head around the the concept pretty well but, for those that have lofting experience, is there anything that I should look out for while doing this to make sure that I don't miss anything?

Thanks
Dave
DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
viewtopic.php?f=23&t=29753

Kevin Morin
Posts: 699
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Question on re-lofting my TNT

Post by Kevin Morin » Tue Oct 04, 2016 3:55 pm

DSR, I'm only remarking about one phrase in your post- not the entire post. I appears you're contemplating/planning/considering to redraw the transom/engine mount plumb? That is drawn from the phrase " and changing the transom angle to 90°" in your post.

I'd say that was not a good idea. Outboards' trim settings on the "traveling pin" are all outward/aft/less tuck/"bow up". So, using the manufacturers' most common 12-14 degree rake (aft lean) as a starting point- the engine's running attitude can be trimmed outward!!!

What I understand you plan to do is to cancel the 12deg rake shown in the plans (my eye-ball-estimate) and make the transom plumb!!! ?? If that were to happen even with the engine trimmed under as far as possible the boat will run bow up and will likely porpoise or oscillate around the leading edge of the running waterline?

I'd do the opposite of your idea- I'd rake the engine mount panel (transom area where the engine is located) aft another 10 degrees and make it 22-25 degrees to the bottom. Then if the bow is down when running full out- move the traveling pin up one hole? REpeat until the boat is trimmed running full out. If you do as you're proposing (?) IMO the result will be a bow up attitude when running?

I'm not remarking about the lines, lofting or any other aspect of this planing hull, in your previous post. Please excuse my mis-reading of your post if I've mistaken your remarks?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

DSR
Posts: 270
Joined: Mon Mar 21, 2016 8:11 pm
Location: Allegan, Michigan

Re: Question on re-lofting my TNT

Post by DSR » Tue Oct 04, 2016 5:22 pm

Hi Kevin, thanks for replying.
I understand the need for a 102° (or more) angle from the hull bottom as the TNT was designed by Glen-L for use with an outboard. I apologize for not putting a few more specifics into the question (I just copied and pasted from my build thread to this section of the forum as I felt it was a better place to ask the question) :oops:
I'm actually modifying my TNT with an inboard jet drive conversion and utilizing a drive extension box added to the transom to provide set-back for the jet pump, so for me, changing the transom angle eliminates a lot of math (which for me is a good thing...). With the speeds I'm expecting with the boat, a 90° transom is also more efficient.

Sorry for rambling Kevin but thanks for taking an interest in my question

Dave :D
DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
viewtopic.php?f=23&t=29753

Kevin Morin
Posts: 699
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Question on re-lofting my TNT

Post by Kevin Morin » Wed Oct 05, 2016 11:53 am

DSR, sorry not to be informed before posting- I just looked up the design photos in the Glen-L catalog pages and saw the boat was outboard -so.... remarked about the transom.

I don't think the stern being raked aft is particularly difficult to loft or built and it will have one great advantage over a plumb transom - in any following sea- and that includes and overtaking wake when you drop off step and slow down- the rake aft lifts the stern more than a plumb stern since the waterplane area will increase as the waterline goes up. Therefore as the overtaking wake/swell reaches the hull with a plumb stern- the boat is raised less than if the stern is leaned aft.

It would be interesting to me to see you post here - your engine & drive-line solution design solution?

AS to the lofting; IMO when you extend the framing station spacing- as long as you re-fair the chines, sheer and any other long hull line/surface intersection the hull will come out fair. IF the keel and chines are roughly parallel in the area of the adjacent frames (fore and aft) then the primary shape change to be addressed is the sheer, deck or coaming lines as those upper curves may be affected by the change in spacing where the keel and chines are not if the after bottom is a prism?

Cheers,
Kevin Morin
Kevin Morin

DSR
Posts: 270
Joined: Mon Mar 21, 2016 8:11 pm
Location: Allegan, Michigan

Re: Question on re-lofting my TNT

Post by DSR » Wed Oct 05, 2016 5:24 pm

No worries Kevin, it was my mistake in not providing more info when I posted this.
If you have any interest in the conversion, this is the URL for the build thread I started a few months ago to document the build and the conversion. Not a lot of actual building going on yet but I've got the bulk of the conversion components in hand and I'm pretty sure that I've got all the modifications down in about 30 pages of notes, sketches and diagrams. Once I get the dimensions for frame 1 lofted I'm going to start building. I'm hoping to have the hull built, encapsulated and sheathed by spring.

viewtopic.php?f=23&t=29753

The second post on the thread shows a rough sketch of the plan and profile views of what I'm shooting for.

The build plans show the TNT as a "warped" hull design with the deadrise increasing as you move from the transom forward so the keel is pretty much the only constant between the transom and frame 2. With frames 3 and 2 both stretched a proportional 15.6% or 5" the hull should remain fair from the bow to frame 2. I figured that if I used all the known dimensions from the patterns and put the perpendicular for frame 1 at the revised spacing of 37", and using battens to fair the lines for the chines, sheers and carlings / coamings with the known dimensions I should be able to obtain the revised dimensions where the battens intersect the frame 1 perpendicular in both plan and profile views........at least that's the way I see it in my mind anyway.
I've never lofted a hull before so that's why I posted this question, to see if I'm missing anything in the process.

If there's anything that sticks out to you or any questions please let me know

......and there I go rambling again.... :roll:

Thanks Kevin
Dave
DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
viewtopic.php?f=23&t=29753

Kevin Morin
Posts: 699
Joined: Thu Jan 24, 2008 11:36 am
Location: Kenai, Alaska

Re: Question on re-lofting my TNT

Post by Kevin Morin » Fri Oct 07, 2016 10:00 pm

DSR, thanks for the link to your project post, neat (too fast for me: but Neat) project. I don't fully understand the '61 flat bar's roll entirely but I've build a couple of 454-3Stage (8" dia) Hamilton jet sleds (welded aluminum) and would love to see more of your integration the pump in your design.

I agree that framing changes could result in fair lines of the hull, my caution is that wooden frames (speaking transverse) are not thin, therefore the 'point' or line of intersection a hull long, chine or other panel seam needs to be re-faired. The primary reason is the lofting point could be the forward OR after face/plane/side of any given frame.

So is a frame is 3/4" thick there is a forward and after plane to the xverse. That is quite a bit of difference in lofting - the line/batten could intersect the forward edge/surface of each xverse OR it could intersect the after plane or ... the middle of each.. All three conditions may result in unfair curves- it depends on the lofting to clean up those lines. Maybe that should be stated "fair" those points -not "clean up?"

When time allows it will be interesting to watch your pump integration into this hull. It seems the result will be similar to the tiny jet sprint racing hulls that are so popular DownUnder?

Cheers,
Kevin Morin
Kenai, AK
Kevin Morin

DSR
Posts: 270
Joined: Mon Mar 21, 2016 8:11 pm
Location: Allegan, Michigan

Re: Question on re-lofting my TNT

Post by DSR » Sat Oct 08, 2016 10:44 am

........and this is exactly why I love being a part of this forum!!!
Hi Kevin,
First, you're absolutely right about fairing the frames for the longitudinals. I hadn't thought of the process until you asked. Looking at it I would think the best course would be to cut the notches in the frames on the side that requires the least amount of material cut out and then remove material to fair the notches when fitting the longitudinals ( the same way the sheer clamp notches would be faired when fitting the clamps between frame 3 and the breasthook). In example, for the sheers, cut the notch on the forward side of frame 1, but cut the notches on the aft side of the frame for the chine logs because of the difference in the angles that the logs intersect the frame compared to the sheers. A lot easier to remove material than to add it, if I'm looking at the process correctly.

.....and the 6061 is being used to fabricate a combination mount flange / adapter assembly that will allow me to mount the pump as one assembly in the hull. This will be in 2 pieces. The first being a mount flange for the intake side of the Yamaha cast duct housing with a receiver groove to flush-mount the housing and weld it into the flange.The second piece will weld onto the output side of the duct housing to allow me to bolt the Honda pump assembly to the duct housing and will also have a mount flange around it. The rear edge of the intake flange and the bottom edge of the output adapter flange will be welded together to create a one piece "knee" (for the lack of a better term) to flush-mount and thru-bolt into the dropped keel running pad I'm adding to bottom of the hull, and thru-bolted into the end cap of the drive extension. The intake flange will also be relieved on both sides to bolt on a couple CNCed aluminum intake fins and a pad machined into the back edge to mount the front edge of the ride plate assembly (that'll keep the mill, and the welder, busy for a couple minutes....... :D )
I hope all the babbling makes sense and if you see any issues with my plan of attack on any of this please let me know!

Thanks for your interest and help on this Kevin!! :D
Dave
DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
viewtopic.php?f=23&t=29753

DSR
Posts: 270
Joined: Mon Mar 21, 2016 8:11 pm
Location: Allegan, Michigan

Re: Question on re-lofting my TNT

Post by DSR » Sat Oct 08, 2016 1:18 pm

I also scanned this VERY, VERY crude sketch of the flange / adapter assembly, if this helps......
Attachments
Jet pump mount flange and adapter assembly draft.jpg
DSR Performance - Home of yet another jet TNT build :D
Codename "Just A Little....."
viewtopic.php?f=23&t=29753

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