Modified pad....

[Superdave]

I have a Hydra-Sports X-270. 17'6" with a 2.4. When running WOT the boat has an incredible amount of bow lift. I know how "flat" an Allison runs due to the slight "hook" at the rear of the pad. I looked at my pad and noticed it is not flat. It has a slight "vee" at about 15 degree angle from the centerline to the outside of the pad. Now my question. I am rebuilding the transom this winter and was wondering if I should flatten the pad. I would also like to see a pic of the lip on the rear of an Allison. Should I :
1. flatten the pad
2. add a lip to the rear of the pad to make it run flatter
3. do one and not the other
4. just fix the transom
Thanks,
guys

[Tony Brucato]

I added a 10 1/2 inch wide flat pad on my 19' Hydra-Sports.

I don't know how much that helped the performance because I also added 2 pairs of lift strakes and removed a couple hundred pounds from the boat.

I tried adding the Allison type lip to the rear of the pad and had bad results. I had to lower the engine several notches just to regain water pressure. Handling and speed were bad too.

I added the lip 26" forward and plumbed in aeration behind it. That helped in a big way.

I built my pad and strakes out of Sitka spruce lumber and epoxied them in place. Glassed in and faired using West System epoxy.
It was a lot of work even with the boat upside down.

If I had to do it again, I would have made the pad wider.
http://brucatosvs.com/pad1.jpg

http://brucatosvs.com/pad2.jpg

[tombrown]

Tony, please tell us more about the aeration. What do you use as an air supply for the aeration holes and how many holes are at the back of the step?

By the way, thanks for the great pictures and for sharing your modification.


Thanks again,

Tom Brown

[Talon2.5]

tony thanks for the pics i enjoyed that one and the airation is definately a winner in the modification, i have the airation steps in my talon also



skip

[tombrown]

HEY SKIP, I'M OVER HERE. CAN'T YOU SEE ME WAVING MY ARMS FRANTICALLY?

So what did you use to pump air out the aeration holes?

[Tony Brucato]

I don't use a pump. By locating the holes behind my wedges I get a natural siphoning action as soon as the boat is moving. I haven't put a vacuum gauge on it, but it will put a hickey on your thumb!

Hoses (http://brucatosvs.com/pad3.jpg)

I cut some wedges 3/32" high by 1/2" wide and shaped them for my pad. BEFORE epoxying them in place I drilled and tapped for four 1/4" ID pipe nipples at a 30 degree sweep back. I located the openings half under the wedges.
After epoxying everything in place I plumbed hoses as high as I could under the rear deck.
Using small flathead screws and epoxy I mounted the wedges.

I hadn't thought about using an air pump, but it might be interesting to bring along an air bottle to shoot through the hoses and see what happens.

Wedges (http://brucatosvs.com/pad4.jpg)

[tombrown]

Ahhhh. So you're drawing water through those tubes?

[Tony Brucato]

It's pulling air, not water through the tubes.

At speed there is a low pressure area created behind the wedges that pulls air from the bilge and through the hoses. The same effect as blowing air through from the inside.

The only time you will see water in the hoses is when the boat is at rest, then it will be level with the waterline. Oh yeah, when you're backing up water will rise much higher in the tubes. I guess you could put in check valves to stop that.

[Techno]

Try ram air to the hoses!

[ShipBear]

I have a 19' PickleFork Tunnel, think something like that might do me some good..? Where and how did you put them on your Hull.?


Thanks Larry
You have a picture of yours.. :D

[Liqui-Fly]

In labs we use an aspirator hooked to a faucet when we don't have house vacuum.The vacuum ceated would be equivalent to the vapor pressure of water which is temperature dependent. If the water is 70 degrees the vapor pressure (vacuum) would be approximately 19 mm of Hg.
David

[tombrown]

Thanks for being patient with me, Tony. I didn't realize that the hoses are all open to the air on the other end. I was thinking the pad outlets were connected to the vents behind the wedges. I confuse easily.

My idea was to build a large sheet metal hood over the splashwell such that air rams into it at speed. This hood would funnel into a 1 inch copper pipe which would run down to a manifold in the bottom of the boat with about 6 - 1/4 inch vents in the pad. The thing holding me back is that I'm worried bugs and skeeters will ram down the funnel and plug up my progressively smaller tubes. I suppose I could blow them out by sending compressed air back up from the pad vents.

I really like your idea. I could just vent the hoses to the splashwell and not worry about water backing up. A small air filter would keep the animals out, too.

Am I right to assume that with a stepped pad, the boat will ride on the two rear edges of the steps causing an increase in nose pitch? How did you come up with the 26 inch size of the rear step? Is the step 1/2 inch high? Does it provide as much bow lift as it looks like it would?

Sorry for all the questions. I can't tell you how much I appreciate you sharing your ideas.


Best regards,

Tom Brown

[Tony Brucato]

Tom,

I located the steps through trial and error. Using 5 minute epoxy I glued the precut wedges at different locations right at the boat ramp. You can use a propane torch to carefuly heat up the wedge. This softens the epoxy so you can pop it off.

All this does is give you an idea where your balance point is. Adding the aeration might change your results. After doing the final installation with plumbing and such, I had to tweak my work
with the two little wedges that you can see just off the pad and forward of the transom a couple of inches.
http://brucatosvs.com/pad1.jpg

Pictures and video of your boat running at speed will help you determine a good location for your step. The wedges that I put on are about 2 or 3 inches aft of where the pad meets the water, adding bow lift and aerating the running surface. It's not a very scientific method I used, so I'm sure that there's a better way to do it.
http://brucatosvs.com/strollin.jpg

Your idea with a scoop should work too. But if I had a nice shiney new boat I couldn't stomach cutting holes in the bottom.

BTW The wedges I made are only 3/32" high.

[Superdave]

Good info and pics. I won't have the advantage of turning it upside down. I can get it off the trailer. I also plan to reinforce the transom with some aluminum & brackets running towards the front. Any ideas? I saw a few in an earlier post.

[Talon2.5]

hey tom :D wasnt ignoring you his is more trick than mine, the ones in the talon are a step in the hull about half inch and about 2 feet i think ahead of the transom, it's a factory done step in the talon but i'm glad there in it

skip

[tombrown]

What would happen if Tony put sides on his pad step? Perhaps some 1/4" material could be glassed to each side of the step so it would seal to the water better. Wouldn't that increase the amount of air he would draw through the aeration system?

PS - thanks for being a good sport, Skip. :)

[Tony Brucato]

You must be reading my mind Tom! I've had plans to do something like that for some time now. I was thinking of aluminum extrusion screwed along side the pad, similar to "Speed Rails". It should make the aeration more effective and keep more of the water under the pad.

I might also borrow your idea to pressurize the hoses for extra aeration. Good idea!

[Firestarter]

In 1981 Challenger boats (the canadian built ones)had an irated bottom similar to what Tony is doing. Though they had the airation holes in the back of the step, and the step was part of the pad.
A point of interest might be that these boats had 21 1/2 inch holes across the the pad. behind these holes is a common chamber, that is fed by two 3 inch PVC pipes run across the floor and up into the motor well.
This modification (they were built this way, in the mold) was worth a good 5-7 mph.
The air moving through these huge tubes was tremendous, you can hear them howl when the boats are over 80mph.


RT

[Tony Brucato]

I'd love to get a look at that Challenger.

I believe the speed numbers, by closing off the 4 hoses in my boat, I will lose 2 mph!

[Firestarter]

Tony very few were built, but those that were are kinda collectors items around here. I am currently trying to get my hands on one that has a pair of Evinrude RS motors on it and flirts with 100mph, not to shabby for 1981 technology!.

I cannot think of where you would get a picture of one, I will try, but the boat that I speak of is in a barn, for the winter nap.

RT

[Techno]

Do they act like deer whistle, like on trucks? Nothing like hitting a deer at speed!