Vertical trim tab (Surfgate) testing results

[High altitude]

I finally have had time to build a completesummary of what I have done so far. Foranybody that has not read my previous posts, I have been trying to build a similarsetup to the Malibu Surfgate on my 99 Ski Nautique (closed bow, direct drive,designed for skiing primarily). I haveconcentrated my design efforts on building a port side wave because that willbe the hardest to achieve with my boat (RH prop rotation and it is noticeable). My general goal is to have a systemwhich allows me to fully use the boat for skiing the course while allowing methe option to fill a rear fat sac and use the “gate” to select between port orstarboard. It has to be retractable toallow fully maneuverability at slow speed (under 5 mph). I would like both sides to surf equally wellbut realize that the starboard side might always be a bit better. The specific goals for my prototype are:
1. Eliminate the need for a side sack due to space and time needed forreconfiguration between goofy and regular.
2. Build a better wave. Longerpocket for both sides, more definition for the port side.
3. Reduce the lean and increase maneuverabilityat slow speed versus a sacked out boat.
It is important to base these tests on what Ihave for my current setup thus I have included that information as well. Here is a summary of all my testing so far:
Baseline:
Weight: 750 lbs fat sac in center rear of the boat. 260 lb on surf side. Optional 320 in front storage compartment ifthe boat is actually loaded with people sitting closer to the rear (hardly everused).
Crew: Driver (160) +on average, 1 other (160 lb) sitting on jump seat behind driver seat or onobserver seat (or two of my 80 lb children)
Board: Inland Surfer Blue Lake
Rider: 150 lbsintermediate
Gate: None
Speed: 8.5 mph
Observations:
Very surfable on starboard (goofy) side. Pocket extends from right behind the swimplatform to about 10 feet back. Decent shapewith plenty of push. Port side is fairlyweak. Even when weighted it is not realclean and lacks height/shape. Barelycan go ropeless and it is not fun because the pocket is tiny. The more weight the better the wavebecomes.

[High altitude]

The prototype: Simple2x4’s connect to the swim deck using 3/8 thru bolts. The 2x4’s have stainless steel hinges on theends connected to a 8x22x1/2 inch stained and sealed pine board. The hinges allow the whole thing to adjustangles if and when I decide to move the 2x4s. This will allow the angle to be adjusted.

[High altitude]

Test 1

Test 1:
Weight: 1000 lbs fat sac in center rear of the boat.
Crew: Driver (160)
Board: Inland Surfer Blue Lake
Gate: 8 x 22” at 40 degree offset from hull. Because of the camber of the boat (mydefinition -- the curvature of the hull when looked at from above…similar tolooking at a cross section of a wing) the actual offset is more like 20 degreesfrom the relative forward motion. TheNautique hull for that year group has a pretty severe “taper”.
Speed: Tested at 8.5mph nominal starting speed as this is the default speed when normally surfingusing side weighting versus a “gate” approach. When through .3 MPH increments to 9.8.
Observations:
Not very surfable. The delayed convergence was noticeable but did not allow the wake tobuild up much. Could go ropeless for avery short time but there was really no sweet spot. The wave actually had nice form and was morecleaned up then simply adding weight to that side. The gate was just under the swim platform butthe platform was under water. Thus, afair amount of water was actually going over the top possible reducing theeffectiveness of the gate. Rudderauthority is very poor and at idle I can only make right turns. Obviously, this reiterates the need for aretractable device when I make the final version.
Follow-on work needed: Increase size of gate so water does not go over top.

[High altitude]

Test 2:
Weight: 1000 lbs fat sac in center rear of the boat.
Crew: Driver (200lbs) plus child in observer seat (80 lbs)
Board: Hyperlite Landlock (much slower than Inland Surfer –kind of a worst case board but it is my go to board for beginners)
Gate: 12 x 22” at 40 degree offset from hull. (same)
Speed: Tested at 8.5mph nominal starting speed as this is the default speed when normally surfingusing side weighting versus a “gate” approach. Went through .3 MPH increments to 9.8.
Observations:
Still not very surfable! I thought the size of the gate would help and it did when looking at thewave. You could clearly see the delayedconvergence and the port side was more built up. There was zero push to the wave and goingropeless was worthless. Although I hadchanged boards for this test I have ridden both boards enough to know that thiswave sucked on either board. Speedincrease from 8.5 tended to reduce the size of the wave without addingpush. (That is consistent with my normalsetup) The wave was also more “angled” than usual. What I mean by this is it was not going back as far but instead was more perpendicularto the boat. I thought this might bemore like an ocean wave but in the end it was no good. This is odd as I thought on the Malibu’s ittended to do the reverse. Maybe the gateis at too much of an angle or not enough. Hard to tell.
Follow-on actions: Add weight to surf-side, adjust gate angle.

[High altitude]

Test 3

Test 3:
Weight: 1000 lbs fat sac in center rear of the boat. 260 pounds on surf side (port)
Crew: Driver (200lbs) plus child sitting on rear sack on surf side (80 lbs)
Board: Hyperlite Landlock (same)
Gate: 12 x 22” at 40 degree offset from hull. (same)
Speed: Tested at 8.5mph up to 9.8 mph. Went back to 8.5 formajority of ropeless surfing
Observations:
OK. Getting better…but now the whole question of whether to build a real hydraulic actuated gateis starting to come into question. If Ihave to weight the boat to get a wave, I’m right back to where I was. The wave seemed OK. It was still more perpendicular but it wasmuch bigger. I could ride ropeless andcould move up and down the wave. Stilllacked the push I usually have on the other side. Bottom line… still not what I would want. l did notice some lean back in the boat. This caused the gate to be lesseffective. The top of the gate wasclearly out of the water so it meant that there was probably only 7-8 inches inthe water. I could not see the delayedconvergence as clearly as in test two. I could add some depth but am afraid that this will make it too deep andaffect the ski wake or affect the surf side when I actually have one installedon each side.
My thoughts now haveturned to the stepped hull of the Nautique. Currently, the gate does not trap the water that comes from the pocket(or cutout in the hull). See picture 3. I might have to deal with this and see if ithelps. The problem is how to deal withthis but not affect the ski wake. I havelooked at the back of the boat at 30 mph and this cutout is actually above thewater but I wonder what the effects are. Suddenly I have gotten pessimistic that I am going to get the results Iwant. The other approach I could takeis to move the pivot point of the gate (where it attaches to the stern) alittle closer to the center of the boat to ensure I capture whatever water iscoming thru the cutout.
The angle of thegate could be an issue as well. Frankly,I’m not sure whether it needs more or less. I have come up with a modification I can do to my 2x4s so I can adjustthe angle before each run.
Any othersuggestions?
Follow-on actions: Adjustgate angle and try various shapes of “new” gates.

[fischris]

Thank you for testing DIY surfgate - I'm very interested to do one in my SAN 230

[jjsaustin]

I think you are on the right path by adjusting the angle of the gate and making sure all the water has a smooth transfer from the hull to the gate.

Also, I don't see pic 3 you referenced above.

I am still working on my temporary setup. It is a little more difficult since I have a fiberglass platform and I don't want to drill holes just yet..

Hopefully, the weather will cooperate this weekend and I will get to test it.

Keep up posted!

[High altitude]

Sorry for the post quality. I've been travelling and typing while on the plane. I then cut and pasted from MS Word but the formatting got jacked. Also the pics would not copy so I had to reinsert after I had written the post. Thus, the picture to look at is #1. If you look at this picture...on the far right part of the hull (under the Nautique sticker) you can see a hull "cutout" starting. It gets progressively bigger. The pic does a poor job of capturing what happens at the end of the boat. By that point, the cutout is a 3 inch L shape (it's actually an L shape but with a 90 degree rotation clockwise). This allows water to pass behind the gate. It is possible that the surfgate concept will only work with boats that do not have this design.
Looks like it will be cold this weekend so I winterized my engine (low of 28!!). I left it on the lift so possibly the weekend after I can take it back out and test some of these ideas. I have come up with some other ideas for some weighting options if this does not pan out. -Marc

[TRBenj]

the picture to look at is #1. If you look at this picture...on the far right part of the hull (under the Nautique sticker) you can see a hull "cutout" starting. It gets progressively bigger. The pic does a poor job of capturing what happens at the end of the boat. By that point, the cutout is a 3 inch L shape (it's actually an L shape but with a 90 degree rotation clockwise). This allows water to pass behind the gate. It is possible that the surfgate concept will only work with boats that do not have this design.

You are referring to the tapered chine. To my knowledge, every flat bottomed boat that CC has built since 1982 (ie, not the v-hulled BFN, Excel, Fish, etc) has a tapered chine. Every Ski Nautique from the 2001 forward certainly does.

[jjsaustin]

Maybe you will have to angle the gate to catch the water from the chine.

Lots of experimentation, but the results well be worth it!

[High altitude]

I will move the gate to catch the water currently being "missed" by the chine. I have become realistic though...it might never work. Hull design is a combination of art and science and if the fluid dynamics don't work... they don't work. I have not given up hope yet.

[jjsaustin]

Well, I finished my temporary surfgate install. Based upon your results I located the gate to catch most of the water from the chine. Initially I made the gate vertical. Based upon the results, the next version may be tilted to line up with the multiple hull chines. I hope to test it out this weekend. Below are my pics.

[High altitude]

Looks good. What are the dimensions? I can't wait to hear about the results.

[jjsaustin]

The dimensions are 10x21.

I will post results this weekend.

[jjsaustin]

Well my first attempt worked out OK, but there appears to be a lot of room for improvement.

Recall my tab is vertical and was flush with the bottom of my swim platform. As a result there was a lot of water spraying over the tab.

We did not get a pic of the spray and did not have a lot of time to experiment. I had to squeeze in a couple ski runs, wakeboard runs and goofy wakesurf runs for the other people on the boat. Initially I filled up both rear ballast tanks, but the best wave was obtained when I just ran with full port ballast an no starboard ballast. I think filling the starboard ballast just pushed the tab further below the water and did not fully delay the convergence.

The wave was much better (see pic below), but still not as good as the goofy side. The wave still needs to be cleaned up and increased in size.

Me second take will include a higher gate (which should allow me to add fill both rear tanks for more ballast and increased wave size). I will also angle the tab and put a lip on the top. This should reduce the spray. I also want to make the tab easier to remove. Hopefully, I will be able to get pics with and without the tab for a comparison and try to dial it in.

I'm working on the gen2 tab and I hope I will get to test it tomorrow.