Hull Mods - Vee Pad

[microbream]

Hi Guys,
I thinking off turning my vee hull into a vee pad. I want the hull to climb onto this pad at WOT and hopefully get me a bit more top end speed.
Keep in mind this is a variable deadrise FG hull only 8foot in length. I have found a 1995 patent that gives me the basic pad dimensions per hull size and i intend to be running in the 40mph spped range.
Does this sound like it will work or should i use strakes as well?. I understand chine walking issues may be introduced.
cheers
microbream

[Yellowjacket]

Depends on how much power you have, but for the speed range you are talking about you should look at the Dillon boats, they work well and are getting a bit more speed than you are looking for. Eight feet is a pretty small boat but with a pad it should be better than a deep V.

Rather than just copying something and hoping it will work, you would do well to get Jim Russel's book on the design of tunnel hulls and padded V hulls. His software would do the job for you but a lot of people don't want to spend the bucks for the program. If I was designing or modifying a hull the amount spent is probably well worth it.

You can get a copy of the Sativsky speadsheet that Dingo Tweedy did and put in your parameters and can figure out if you are going to have a porpoising problem, but chine walking stability is something that you can't just calculate with a rule thumb.

[zul8tr]

I agree on Jim Russel's book and software that is mentioned above. Here is the link

http://www.aeromarineresearch.com/about.html

[JohnsonM50]

I agree on Jim Russel's book and software that is mentioned above. Here is the link

http://www.aeromarineresearch.com/about.html

My experience with V's is only in use. I had a 16' Larson deep V with strakes & on it. The trouble I had most was keeping it from leaning one way or another & also found it to speed up when laying over in a wide turn that put it closer to flat, It was something that could have used a pad. I saw a home made deep V testing a few years back, it also had strakes. It was about 8 or 9'. I was racing it & saw that if he could have held it in a straight line for more than a few seconds it would've been pretty fast, It would get going & fall off into a turn semi out of control. Of course that could've been a driver issue From there Id think a pad that rides flat on top end & stabilizes the boat could give you the best of what the boat is capable of.

[Fastjeff57]

I've done this excercise--twice--and my advice to you is: Don't! A hull that short will chine walk like crazy on you.

Jeff

[microbream]

I've done this excercise--twice--and my advice to you is: Don't! A hull that short will chine walk like crazy on you.

Jeff

would not widening the pad make it less likely to chine walk? but obviously slower

i may make a bolt on aluminum pad and play around with dimensions to reduce chine walk and increase top end speed

[Fastjeff57]

It didn't on mine. The pad actually slowed the boat down a few mph until I put a bigger motor on it. And it caused bad cavitation on plane off.

Of course, that was just my experience.

Jeff

[JohnsonM50]

There's no one thing, the pad would have to be right, the motor & props all reset & retested The weight & its distribution re-considered & the combination of things is how it could potentially work. I do it all the time, try something off the wall & find often it should go back on the wall You should research what zul8tr posted. If it looks good from there a temporary test pad of small to larger increments would be a reasonable way to go. If the hull has hard chines then chine walking can have a more drastic reaction so of course test with care. Some padded Vs are real good & since your not trying to go 'warp speed' you might get somewhere.

[microbream]

There's no one thing, the pad would have to be right, the motor & props all reset & retested The weight & its distribution re-considered & the combination of things is how it could potentially work. I do it all the time, try something off the wall & find often it should go back on the wall You should research what zul8tr posted. If it looks good from there a temporary test pad of small to larger increments would be a reasonable way to go. If the hull has hard chines then chine walking can have a more drastic reaction so of course test with care. Some padded Vs are real good & since your not trying to go 'warp speed' you might get somewhere.

Yeh thats what i will do, i will try to get a copy of bill russels book and design a pad using his principles. Might be fun to bolt on a test pad and see if a get some improvement. When you think about it it once on the "pad" you should reduce form drag from you gearcase and viscous drag from having only the pad contacting the water.
anyway got to first fire up my 10 ci Suzuki, she has been well and truly 'worked', i am expecting big things from this little motor.

[Jimboat]

The sizing of a pad can be designed for the specific hull dimensions, weight, HP, etc. (Duplicating a pad from one hull on a different hull might not work out as well).

A proper pad design provides a much improved hydrodynamic lifting capability, resulting in more speed for less drag. But it's a compromise, as dynamic stability is often sacrificed. A safe performance ride will depend on, among other factors, the speed that you want/expect to be going while on the pad, total weight of complete fitted hull (with engine, fuel, passengers, payload, etc), deadrise of pad, planned angle of attack of the pad and AofA (trim angle) of the hull itself. From analysis of these and other design factors, the dimensions of the pad can be optimized to support the hull and to maintain a safe dynamic balance of the ride.

Note that with heavier boats the pad area available becomes more limited in its ability to provide a significant portion of the hulls required Lift. In these cases, lifting strakes can often used also, providing additional lift as well as uncompromised stability. In smaller, lighter boats, the pad can provide up to 100% of the lift...this is harder to do with heavier boats, and so the design trade-offs are often not as beneficial.

Have a look at this article on "Why does a Pad make a Vee Hull Faster" and paper on "Vee Pad Analysis & Optimization"