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.....    ) 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

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

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

That little thing is bad ass!


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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.

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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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

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

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! 

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.

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......

Thanks Joe,
Dave

Awesome. I was wondering what happened with this super neat project. Cant wait to watch your progress and see this thing done

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!!

Dave

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