Need some help on my mini jet mod-VP build

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DSR

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« on: July 10, 2017, 07:04:12 PM »
Hi everyone;

I'm Dave from DSR Performance in Michigan and a new member to the forum.

I am currently finishing up my design for a 12' 6" mini jet mod-VP (my own personal bit of insanity.....   :screwy: ;D) and I'd like to ask for some help with the proper design for the pump intake section to make sure the pump stays loaded at higher speeds.

I've done a ton of research and either I'm looking in the wrong spots, or there just isn't much info on this subject, but I don't want to start building until I'm confident that this little bugger will perform the way I want it to.

I have the hull lofted and modeled so I have all the dimensions and this is the last piece of the puzzle before the fun begins.

Any and all help would be greatly appreciated!

Thanks
Dave



DSR

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« Reply #1 on: July 10, 2017, 08:57:02 PM »
Sorry guys, I should provide a few more details to give everyone a better idea what i'm messin' with.....

The hull is 12' 6" long with a 5' 0" beam and set up for the powertrain from a 2004 Honda R12X PWC donor. The center pod is 12" wide and extends 12" beyond the transom as a drive extension pod (similar to a Southwind TD or Kachina Condor hull). The keel centerline sits 9/16" below the bottom edges of the sponsons at the transom. The pump intake is 15" from the lead in to the front of the shoe assy. The lead in on the intake is also 21" from the back edge of the extension pod.

Any ideas on this would be great.

Thanks again
Dave

08chevyguy

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« Reply #2 on: July 11, 2017, 04:32:15 AM »
Welcome to the site. And im sorry but i cant help ya with your questions. But looks like an awesome project and i love the hull design btw. Looks awesome. Be sure to post up some pics of thr whole process whenever you start. And im sure somebody will put their 2 cents in sometime soon

DSR

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« Reply #3 on: July 11, 2017, 06:27:51 PM »
Thanks 08Chevyman,
I've already spent WAY more time and effort on this bugger than I probably should have so I really appreciate the compliment!  :)


« Last Edit: July 15, 2017, 06:38:57 AM by DSR »

mash on it

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« Reply #4 on: July 11, 2017, 09:27:07 PM »
So, I don't know much about mini jet mod vp hulls or whatever.

Here's what I do know- Them Honda turbo skis would run 70 mph or so 'out-of-the-box'.

With the HP per Lb, or Thrust to weight ratio, I think the intake, mounted the way Honda did it, would still perform. And at 70 mph,it would still be a handful in that mini boat.

The Aussies and Kiwi's have already done it with Kawi/SeaDoo/Honda jet power plants in 12'-ish  aluminium 2 seater boats.

here:

and:

and:



just my $0.02

Dan'l
CJ/RR 212...under construction  "Pistol Annie"

seapat

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« Reply #5 on: July 12, 2017, 12:06:40 PM »
Those look like fun. Go karts on the water

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« Reply #6 on: July 12, 2017, 12:28:17 PM »
That little thing is bad ass!


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DSR

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« Reply #7 on: July 12, 2017, 04:22:05 PM »
Hi Dan'l
yeah, the Honda turbos evidently run pretty good from what I've heard. My donor was a wrecked one with 66 hrs on it that I got a good deal on. The ski is 842 lbs and has a pretty deep V hull so it should run REALLY well as a 650 lb tunnel hull.   :)
And if, for some ungodly reason, it's not enough, I can tweak the boost 5 lbs, add water / meth injection and go from 165 hp to 240+...... 

Unfortunately, the pump intakes on these are molded as part of the ski hull so I'm adapting the pump to a aluminum intake duct from a Yamaha GP1200 ski (which has a flat intake).
The river minis are pretty frickin cool for sure, but the hull design is completely different from the tunnel I'm building and I'm not sure if the flat Delta's that they use would work well on it, unless someone can tell me differently?

Hi seapat and Blue2184, thanks for stopping by.

Yeah, some of those river minis are pretty badass for sure!

This is the ski I picked up to power my mini. 1235cc of DOHC EFI dry-sump 4-cylinder Honda with a turbo and air-to-water intercooler. I think it should be a pretty cool little setup when it's done  ;D

Thanks!
Dave
« Last Edit: July 12, 2017, 08:06:32 PM by DSR »

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« Reply #8 on: July 19, 2017, 07:43:55 PM »
Hi everyone,

I've been working on the keel design for the intake on this little bugger and I've come up with a couple possibilities and I wanted to post them to see if either would be a workable design for the hull? With the Yamaha GP1200 cast aluminum intake duct I'm using being flat both front to rear and side to side and has a pretty big mount flange surrounding it, it looks like I'm kinda relegated to running a flat keel

The first design is 11" wide, drops ~ 3/4" below the keel center line and runs forward 5' 6" from the end cap of the drive extension. The bottom of the keel is level and flat for 3' 3" from the end cap with vertical side wall, and then gently tapers and slopes with the side walls angled as shown, to a point on the original keel center line with a resemblance to a "NACA" shape.




« Last Edit: July 21, 2017, 10:02:49 AM by DSR »

DSR

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« Reply #9 on: July 19, 2017, 08:07:17 PM »
The second design is, what I guess I would call, a more traditional looking drop keel. 6' long with the same drop and 11" wide where it attaches to the hull and the side walls angle in to 9" wide at the bottom surface of the drop keel. It runs level for 3' 3" forward and then gently tapers and slopes again to a point on the keel, but with much softer, more "bulbous" shape.

At this point, I'm leaning more towards design #2 as a better design for the job, maybe even incorporating the vertical side walls from design #1 to create sharp chines for the drop keel?

Again, any help with this problem would be greatly appreciated!

Thanks
Dave




« Last Edit: July 21, 2017, 10:03:19 AM by DSR »

Six-Oh-Nine

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« Reply #10 on: July 23, 2017, 11:42:52 PM »
Don't know if I'd do such an abrupt change in the keel to a flat surface. Personally, I'd transition into a radius and then build up the intake on the pump so as to help keep the pump loaded. Also... are you trying to work with a keel parallel to the tunnels? Or something like a negative keel like a Crusader? Or a positive keel like a Daytona? It looks pretty parallel, which makes quite a difference in how you address loading the pump from the keel.


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DSR

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« Reply #11 on: July 24, 2017, 03:49:33 AM »
Hi Six-Oh-Nine,

I would call this a negative keel as the keel stays level for 74" forward of the transom and the tunnel roofs and sponsons have a slight angle so the distance from the keel to the tunnel roofs increases as you move forward from the transom

I'll include a Linesplan of the hull that gives a good idea of the relationship of the keel, tunnel roofs and sponsons....

Thanks for your help!!
Dave


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« Reply #12 on: July 24, 2017, 07:54:28 PM »
Six-Oh-Nine, I also took some pics of the pump intake to give you an idea what that looks like.

The intake is flat both front-to-back and side-to-side and is 23" x 7". With a 1.5" wide aluminum flange I'm fabbing to surround the intake and mount it into the keel, the outside dimensions are 27" x 10'. The front of the lead-in to the intake will be about 5" from the front edge of the flange.

I've messed with the idea of doing a radius drop keel previously but i'm having a hard time visualizing how to do it with this intake and also the transition from the original keel to a radiused drop keel both at the front of the drop keel and transitioning into the intake to properly load the pump. One thing I can easily do with the mount flange being CNC'ed out of 1" thick 6061 stock is that I can form a radius from the edge of the intake to the outside edge of the mount flange on the sides, if that makes sense?

Thanks again.
Dave


« Last Edit: July 24, 2017, 07:59:32 PM by DSR »

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« Reply #13 on: August 19, 2017, 05:05:45 PM »
Hi there,

Welllll.....I've been doing a ton of searching and annoying the hell out of anybody I can get in touch with on this little issue I'm dealing with and I think I came up with something that might work, but I wanted to show it to the members here that would know and see If something like this would do the trick?

This is just a crude rendering but I think it'll show what I'm thinking. I did some cleaner pics but the transitions are so subtle that radius keel blends right in....

A radius keel added to the original keel in the center pod - 6.5" wide to match the width of the lead-in to the pump intake and around 5' from the beginning of the transition at the front to the end of the blend into the intake. I came up with about a 1/2" thickness from the original keel to the center line of the radius.
(As a side note: I will be fabbing intake fins for the intake also.)

Also, with the center line of the original keel being 9/16" lower than the bottom edges of the sponsons, and the radius keel dropping another 1/2", this will leave it at just over a 1" difference. will that be enough to allow pump loading? 

I'd love to get some feedback to see if I'm headed in the right direction or not?

Thanks!
Dave

« Last Edit: August 19, 2017, 05:07:48 PM by DSR »

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« Reply #14 on: August 20, 2017, 01:39:38 PM »


Hi there,

Welllll.....I've been doing a ton of searching and annoying the hell out of anybody I can get in touch with on this little issue I'm dealing with and I think I came up with something that might work, but I wanted to show it to the members here that would know and see If something like this would do the trick?

This is just a crude rendering but I think it'll show what I'm thinking. I did some cleaner pics but the transitions are so subtle that radius keel blends right in....

A radius keel added to the original keel in the center pod - 6.5" wide to match the width of the lead-in to the pump intake and around 5' from the beginning of the transition at the front to the end of the blend into the intake. I came up with about a 1/2" thickness from the original keel to the center line of the radius.
(As a side note: I will be fabbing intake fins for the intake also.)

Also, with the center line of the original keel being 9/16" lower than the bottom edges of the sponsons, and the radius keel dropping another 1/2", this will leave it at just over a 1" difference. will that be enough to allow pump loading? 

I'd love to get some feedback to see if I'm headed in the right direction or not?

Thanks!
Dave

Hi Dave,

I have a couple thoughts/questions.

The dropped keel in your latest rendering looks way better than the earlier pad design.  If I'm understanding correctly, your dropped keel extends 5' forward of the intake opening.  That's plenty of length and the transitions should be very subtle as to not create drag.  Once on plane, anything more than 2' forward of the intake will be out of the water, but I think it reduces drag on the hit.

How much keel you need is largely dependant on how fast the boat will run and how much horsepower.  The pump needs to be able to process all of water that you are feeding it.  This is a very fine balancing act.  What you design into your mold is simply a starting point.  As you increase horsepower/speed you may find that you could benefit from adding more keel.  Each combination needs to be evaluated on an individual basis.  Using your numbers of 6.5" wide and 1/2" deep, I come up with a 10-13/16" keel radius.  Without having any experience with these hulls and pumps, my gut feeling is that you have designed in a safe starting point.  I don't think reducing keel radius to increase keel depth would be a good idea.

How wide are the lifting surfaces on each side of the dropped keel?  You might need to narrow them to reduce lift.

The pod looks extremely long.  How far back from the transom does the pod extend?  Where is the relationship between the entry/shoe relative to the transom?  The pod does not need to be any longer than the back of the shoe unless you need support for the pump.  If so, maybe consider a step after the pump.

While on the topic of the pod, you need very large radii where the pod intersects the transom.  This area is known to crack.  Not trying to bash on your design, I actually really liked the pod concept until I started working on SWTDs.  The current Placecraft has eliminated the pod in favor of somewhat of a stepped hull.  There is plenty of room to work inside, the pump and primary ride surface are much better supported, and the wetted surface is reduced.  I totally understand if you just need the pod, just give your design the best opportunity for success.  Sharp corners are bad news.

Again, if I'm understanding correctly, you have the lowest point of the outer sponsons 9/16" higher than the flat lifting surface next to the dropped keel.  Depending on how much lift will be generated by the lifting surfaces of the center sponson, I see the following scenarios:  1) you are sacrificing aerodynamic lift without creating an affective seal of the tunnel to the water at the outer sponsons.  2) if the center sponson develops enough lift to actually get the outer sponsons out of the water, the boat could: A) develop a chine walk instability as the hull rocks back and forth from sponson to sponson, B) it could actually unload the pump.

You might want to make your fins removable so that you can try different configurations.

Cheers,

Joe
"I want to roll with my brother Joe" - Joe Bateman - January 29, 1950 ~ November 27, 2013

DSR

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« Reply #15 on: August 20, 2017, 04:04:36 PM »
Hi Joe, thanks for the reply! This is the last detail of the design to hammer out before I start building and it's been driving me to drink more than I already do!  :banghead:

I do feel more comfortable with this last keel design myself after digging around for info, and your feedback definitely helps.it also became pretty obvious that a good starting point is the best I can hope for, but it's a lot better than what I had before.

To start off, the hull is a one-off that I'll be building in African Mahogany and Okoume marine plywood, so I won't have the issues involved from doing it in glass. The pod does look longer than it really is because of the 3D rendering program I'm using skews the perspective. It's actually extends 12" behind the transom to be able to fit the powertrain in the boat and get a good C of G (I determined the pod length based on where the back of the shoe landed). The Linesplan shows a better view of the dimensions.

The bottom of the hull.has a 2 deadrise at the transom, so the outside edges of the center pod are 1/4" higher than the keel, and the bottom inside edges of the sponsons are 9/16" higher than the keel, so a little more than a 1/4" difference (I was planning to test it as-is and if I ended up with chine walk or other weirdness, I was going to try the aluminum angle air entrapment mod on the sponsons). With the radius keel at 6.5" wide on the 12" wide center pod, I'd have 2 3/4" of hull on either side.
The very front of the intake lead-in (about 2" before the front edge of the grate mount in the intake pics) is 8" in front of the transom and 6.5" wide and tapers down to 5" at the start of the shoe radius. The center of the front edge of the shoe is 15" behind the lead-in, so 7" behind the transom. With the intake being flat front to rear and side to side, I was looking to mount the intake flush with the bottom of the center pod with the surrounding mount flange CNCed to match the deadrise angle, and have the radius keel end where it blends Into the intake. Does that sound appropriate?
I did actually design the fins to be bolt-in and changeable for testing, I'm also fabbing an adjustable ride plate (currently planning on 6.5" wide by 12" long.....)

I actually worked with Jim up at Aeromarine Research on developing the design, and running a performance analysis on it, this thing starts trapping air at about 50 mph,.and by 70 it shows that the outer sponsons are clear of the water and it's generating 27-28% of it's lift aerodynamically (which Jim stated as being a pretty high percentage). The analysis also shows that with the stock 165 hp and a conservative 39% thrust efficiency from the pump (sounds pretty low to me), it's showing speeds over 80 mph.

I really appreciate the help Joe and please let me know what you think, or if you need more info.

Thanks!
Dave

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« Reply #16 on: August 21, 2017, 06:50:45 AM »


Hi Joe, thanks for the reply! This is the last detail of the design to hammer out before I start building and it's been driving me to drink more than I already do!  :banghead:

I do feel more comfortable with this last keel design myself after digging around for info, and your feedback definitely helps.it also became pretty obvious that a good starting point is the best I can hope for, but it's a lot better than what I had before.

To start off, the hull is a one-off that I'll be building in African Mahogany and Okoume marine plywood, so I won't have the issues involved from doing it in glass. The pod does look longer than it really is because of the 3D rendering program I'm using skews the perspective. It's actually extends 12" behind the transom to be able to fit the powertrain in the boat and get a good C of G (I determined the pod length based on where the back of the shoe landed). The Linesplan shows a better view of the dimensions.

The bottom of the hull.has a 2 deadrise at the transom, so the outside edges of the center pod are 1/4" higher than the keel, and the bottom inside edges of the sponsons are 9/16" higher than the keel, so a little more than a 1/4" difference (I was planning to test it as-is and if I ended up with chine walk or other weirdness, I was going to try the aluminum angle air entrapment mod on the sponsons). With the radius keel at 6.5" wide on the 12" wide center pod, I'd have 2 3/4" of hull on either side.
The very front of the intake lead-in (about 2" before the front edge of the grate mount in the intake pics) is 8" in front of the transom and 6.5" wide and tapers down to 5" at the start of the shoe radius. The center of the front edge of the shoe is 15" behind the lead-in, so 7" behind the transom. With the intake being flat front to rear and side to side, I was looking to mount the intake flush with the bottom of the center pod with the surrounding mount flange CNCed to match the deadrise angle, and have the radius keel end where it blends Into the intake. Does that sound appropriate?
I did actually design the fins to be bolt-in and changeable for testing, I'm also fabbing an adjustable ride plate (currently planning on 6.5" wide by 12" long.....)

I actually worked with Jim up at Aeromarine Research on developing the design, and running a performance analysis on it, this thing starts trapping air at about 50 mph,.and by 70 it shows that the outer sponsons are clear of the water and it's generating 27-28% of it's lift aerodynamically (which Jim stated as being a pretty high percentage). The analysis also shows that with the stock 165 hp and a conservative 39% thrust efficiency from the pump (sounds pretty low to me), it's showing speeds over 80 mph.

I really appreciate the help Joe and please let me know what you think, or if you need more info.

Thanks!
Dave

So I have the opportunity to learn also, I don't have access to simulation software.

How did you determine your COG location and what was your criteria?

Why do you want the outer sponsons out of the water?

You can always add more to the keel if needed.
"I want to roll with my brother Joe" - Joe Bateman - January 29, 1950 ~ November 27, 2013

DSR

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« Reply #17 on: August 21, 2017, 04:59:03 PM »
Hi Joe,

I ended up buying Jim's Tunnel Boat Design Program and while it wasn't cheap, it generates a lot of good info and the design specs are easy to change to see what works and what doesn't.

Getting C of G with it is just a matter of specifying the type of hull, the dimensions and bare hull weight, and it either generate the C of G of the bare hull, or you can specify it if you know where it's located. All the weights that go into the hull (engine, drive, fuel tanks, batteries, people, etc) are specified by length from the transom and height from the keel, for the center of mass for each item. It also generates Center of Bouyancy. Then with hull shape and thrust it shows all sorts of details on water drag and lift, air drag and lift, centers of the lifts and how those lifts move along the hull through the speeds you specify.from stationary to top speed. It also generates top speeds and shows the amount of power it takes to generate each speed along the scale you give it. It's very cool!

As far as the sponsons, I actually started the design as a low-deadrise warped bottom design (like a flat bottom hull) and then decided midstream to change it into a Mod-VP, so I basically did the same thing that Crusader did to create their tunnels by "cutting" the tunnels into the design. I originally thought to get the sponsons out of the water at speed to reduce drag, but after doing some reading, I realized that it could cause the tunnels to load and unload, generating chine walk. With the sponsons bottom edges being so close to the center pod depth I figured that it may not be an issue, and fixable if it is. There was a surprising amount of drop in water drag when the simulation showed the sponsons leave the water and the hull just riding on the center pod.

Thanks Joe,
Dave
« Last Edit: August 21, 2017, 08:33:53 PM by DSR »

DSR

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« Reply #18 on: August 21, 2017, 07:46:01 PM »
Sorry Joe, I got a little sidetracked.....

As far as my C of G criteria, I shot for putting the C of G just behind the center of air lift at speed, which ended up being 3.8' forward of the transom, so I didn't end up with too much stern lift and unloading the pump, or too much bow-down moment. Unfortunately, this proved to be as much of a game as the radius keel is.
The problem is that the center of water lift moves forward and back at different speeds. Center of air lift moves even more drastically ( in the case of my design, when it starts lifting, it starts about 7' forward of the transom and moves back to about 4' from the transom by 75 mph, and starts moving forward again by about 80 ). While this is happening, water drag, air drag and other bow-down moments are moving the C of G at the same time, so they actually can pass each other forward and back. A lot of this relates to the shape of the tunnels, the "attack angles" of the tunnel roofs and how close to the water the tunnel roofs are, along with the shapes and surface area of the wetted sponson and center pod surfaces.
Basically, a fast and efficient tunnel hull is running on the edge of being unstable at speed. The trick to making this work is making the lift and drag moments move slow enough to able to control it with throttle and trim when running the edge...... :D

Thanks Joe,
Dave

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« Reply #19 on: December 10, 2017, 04:20:30 AM »
Hi Everyone,

It's been a while, but I finally made the time to get a little more fun done on my tunnel hull project.
I got the engine and pump pulled out of the Honda and got a lot of the dimensions hammered out to properly locate the engine stringers for the rail kit I'm fabbing to mount the engine. I'm also going to have a bit of time and effort invested in the pump intake to get the pump and driveshaft to mate up and fitting it all into the hull.

Currently I'm getting ready to loft, or draw the hull out full-size, on the shop floor on a couple 4x8 sheets of plywood to make sure that the data points for the frames and hull lines are correct. I hate to put a time frame on the build, but I'd like to have the bare hull done by this next summer.......maybe......  ::)

Thanks and have a great Christmas everyone!!  ;D
Dave


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« Reply #20 on: December 10, 2017, 08:15:40 AM »
Awesome. I was wondering what happened with this super neat project. Cant wait to watch your progress and see this thing done

DSR

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« Reply #21 on: December 10, 2017, 02:12:44 PM »
Yeah, it's been a crazy couple of months with work and life getting in the way of the fun, which I'm sure a lot of people have the same problems...  :)

But the boat is definitely going to happen. I already have too much time and effort into it to just let it go. Heck, I'm probably more excited to see this little ball of crazy run now more than ever, now that the design phase is pretty well done and the building can begin.

Thanks 08chevyguy!
Dave

DSR

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« Reply #22 on: December 17, 2017, 08:08:12 AM »
Hi everyone,  I have another question....

I've been going over the intake setup for the tunnel hull and I was wondering if there's any intake hardware that works with the radius drop keel to feed the pump?

Okay,  2 questions....  ::)

I'm also thinking that the original intake opening on the intake duct I'm using might.be too large to run higher speeds using the radius drop keel and possibly overstuffing the pump?

I did a quick search and I did find a few grates that actually moves the front edge of the shoe forward and reduce the area of the intake opening along with a shallower entry angle from the front edge of the shoe to the pump (which I feel are both steps in the right direction) but I'd like to find out if my thinking is correct, or if I'm way off base? Any thoughts?

I'm  throwing in pics of the original grate and one of the aftermarket grates that I  found out there on the interweb. (This one shows a loader incorporated into it, but that would easy enough to modify/eliminate if necessary and I'm sure there will be some experimenting involved to find the best combo.....)

Thanks again for the help and thoughts!! ;D

Dave


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« Reply #23 on: January 03, 2018, 07:14:25 PM »
Hi everyone, Happy New Year!!

Well, I'm on to the next step and I thought I'd provide an update......

I got the chance to clear some space on the floor of the shop (my buddy that shares shop space with me calls it the toy box....  ;D ) and put together a couple sheets of plywood, cut some battens out of a 16' piece of pine and started lofting, or drawing out, the hull full-size to verify the data points in the Linesplan. I was happy with the lines generated in the CAD program and I almost didn't take the time to loft it out. Boy am I glad I decided to do it!

The data points from the Linesplan are pretty darn close, but not perfect, and I've had to make a few very minor adjustments as I've been going through the process to smooth the lines out. The lofting has shown some kinks in the hull lines that I still can't see on the computer screen or on paper.

Sorry that the pics don't show the hull lines very well on the plywood, but standing there looking at the hull lines full-size, I have a much better idea of the size and overall look of the hull and I'm more than ready to start building this little ball of crazy.

Thanks for letting me ramble  :D

Dave

 
« Last Edit: January 03, 2018, 07:18:33 PM by DSR »

08chevyguy

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« Reply #24 on: January 03, 2018, 07:26:52 PM »
Im glad that you are still working at it and towards your goal. I love watching this come together amd i look forward to seeing more updates

 


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