Hull Design

[jzangger]

I'm new to the forum and have some general questions regarding hull design evolution. I built a Glen-L Tiny Titan in the early 70's and joined the local club in Sioux Falls. I, of course, didn't race but enjoyed the sport non-the-less. My boat still exists but my mass has increased over the years and the small hull and 10hp Mercury just won't get me up on plane anymore. I'm thinking about building a larger boat that would better support me and possibly my grandson as passenger.

In the early 70's the round nose hydro's were the standard. Now most are pickle forks or tunnel hulls and I was curious as to what the advantages are of the newer designs. I have plans for the Clark Craft Ben Hur which was reported to be a fast and stable boat but I would like something to reflect the current technology.

I've noticed a change is the classes also and I'm not familiar with the new ones. I was somewhat aware of the older A, B, C and D classes but don't know how they compare to the new ones or if they still exist.

Any help would be appreciated.

Thanks

[B Walker]

I'm new to the forum and have some general questions regarding hull design evolution. I built a Glen-L Tiny Titan in the early 70's and joined the local club in Sioux Falls. I, of course, didn't race but enjoyed the sport non-the-less. My boat still exists but my mass has increased over the years and the small hull and 10hp Mercury just won't get me up on plane anymore. I'm thinking about building a larger boat that would better support me and possibly my grandson as passenger.

In the early 70's the round nose hydro's were the standard. Now most are pickle forks or tunnel hulls and I was curious as to what the advantages are of the newer designs. I have plans for the Clark Craft Ben Hur which was reported to be a fast and stable boat but I would like something to reflect the current technology.

I've noticed a change is the classes also and I'm not familiar with the new ones. I was somewhat aware of the older A, B, C and D classes but don't know how they compare to the new ones or if they still exist.

Any help would be appreciated.

Thanks

Short history of the evolution of the picklefork hydroplane:

As boats got faster in the 50's the problem changed from getting lift and getting the boat out of the water to keeping the boat on the water. Picklefork hydroplanes caught on in the larger and faster classes first then over the next 30 years gradually was incorporated into the slower classes.

Somewhere around the high 60's MPH you pretty much need a picklefork. Under 60 MPH the only advantage is in the smaller crossection of the design.

Crosssection is the amount of air displaced by the boat measured in total volume at its widest point. Better said, a thinner boat is faster than a thicker boat because it pushes less air out of the way.

OK, thats out of the way. Now for the meat and potatoes.

If you want to build a modern hydroplane there are several plans and kits available under the "hulls and hardware list"

http://www.hydroracer.net/forums/sho...?threadid=9360

If your just interested in owning a modern style hydroplane for fun or perhaps race at some point then used but not used up boats are commonly available for under 1000 dollars. 1k for a boat in race ready condition is about the cost of materials and hardware alone.

I think more information is needed for people to be able to help you out better.

Where are you located?
What do you weigh?
You want to race or just want to make a "laker"?
What engine are you planning on putting on this?

Brad Walker

[mdaspit]

Here is a pretty nice D boat, check it out, he sells a kit, and now has CNC parts cut out for the plywood.

But, the larger they get, the faster they are intended to go.
Example, Sorenson says the D is "speed to 80mph." (That's a loose quote)

So, if you need a larger boat, but don't want all the speed?
Not sure how the boat would handle at slower speeds, they are designed to handle properly at speed.

Give him a call, he'll know.


http://www.boatracingr11.com/Sorense...lane__kits.htm

[jzangger]

Thank you both for the helpful comments. I enjoyed the building process years ago so would prefer to build again with the aid of my grandson. I am looking at the larger boats mostly from a stability and weight carrying capacity rather than the speed. The little 8' hydro I built would approach 35 on 10hp and realistically I would probably only want to go 45-50 at most. I do have an old MK 20 but would prefer something a little larger to get it on plane with the extra weight. Pickle fork would be nice but I do have the plans for the Ben Hur, just don't know what the general thoughts are on the older design. I have also found Fralicks site so my choices would be between a Sorensen, Fralick, Clark Craft Ben Hur or possibly the Glen-L Super Spartan.

In the early 70's I had joined the local club in Sioux Falls, South Dakota but I don't believe they are active any longer. I really don't intend to race so would just enjoy the "laker" approach to the hobby. I am back in the Sioux Falls area but the lake I used to run on has been restricted to fishing only!

I would be open to any engine that would get us all up on plane easily with my weight of 200 and my grandson probably eventually in the 50-70lb range before I take him out. I'm only familiar with the old line motors and don't know anything about the Yamoto but it sounds reasonable.

Also, just for conversation, I am vaguely aware of the old A,B,C and D classes. Do they still exist or have they been replaced? I've seen other classes listed but am unfamiliar. Can anyone make the comparison and catch me up to speed?

Thanks again,

Jim Zangger

[jzangger]

Sorry, just had another thought. My 8 footer had coamings for the purpose of keeping water out of the cockpit as the wake caught up with you while slowing. I see the new boats all have very high coamings. I'm guessing this is more for the purpose of giving better side load support to the driver in the turns to keep him in the cockpit! Am I close?

Jim

[blueskyracer]

As far as I know a CSH boat could work for you with a Yamato but I really think for the load you are talking about with your grandson you would need a boat like a DSH with a 44 Mercury or Tohatsu motor. I must say that two of you in the boat at once is highly not recomended.

The higher cockpit sides serve two purposes. Stability for the driver and more protection in case of side impact during a race.

[B Walker]

OK, I am a little bit clearer on what your looking for.

It is very difficult to put 2 people in a boat designed for one and get a safe and decent ride.

Tunnel boat designs with a trim/tilt mechanism and a gearbox will service you and your grandson much better. A hydraulic trim will allow you to adjust the boat and get a good ride at a variety of speeds where "fixed" motors only run well in a narrow speed band. A gearbox will allow a forward, reverse, and neutral options where all the motors designed for the ABCD classes are direct drive.

Here is a link for plans for small tunnels.

http://www.dillon-racing.com/

Good luck and keep us up to speed with pics in the "new boats for 2011" thread

Brad Walker

[mdaspit]

Yeap Brad, that looks like the perfect solution...

Looks to be easily built, large enough, fun enough, & designed for a simple motor.

[jzangger]

While I wouldn't object to the possibility of a tunnel I am more predisposed to the 3pt hydroplane. I wouldn't be interested in a V hull as their ride just doesn't look as good as the tunnel or hydro.

I'm still not clear on how the different classes compare. Is there a source for the definition of the different classes? Power, weight, length or whatever the limiting factors are for the different categories. Like I said earlier, I was somewhat familiar with ABC&D but don't know about ASH JSH and others. Do the tunnels run with the hydro's?

Thanks again,

Jim Zangger

[BP125V]

try this

Click on the link at the very top of the portals page on HR.net for the Stock Outboard website. Gives an over view.

http://www.stockoutboard.com/

Bill

[B Walker]

There is no easy way to compare the old ABCD class structure which only had one manufacturer (Mercury) that supported the classes to the current structure which has no manufacturers support and has lots of motor manufacturer options.

The best way to evaluate your needs is by weight and speed range.

With your 200lbs and a passenger your certainly not looking at anything that fits into the lower end of the options. The smallest modern motor that I think would do the job is a Yamato 302 and that would have to be setup and propped just right. A Mercury 30h or larger would also be options.

It seems like your kind of set on a 3 pt Hydroplane. A "D" or larger boat with a C sized motor on it would have the cockpit room and stability to be a good lake racer with 2 people onboard. It could easily be setup to achieve speeds in the high 50's or low 60's and be easy to drive.

No modern hydroplane will handle rough water well. If there are whitecaps of any sort it would not be a very good ride. Tunnels do very well in rougher water conditions. Flatbottoms and v-hulls are the most difficult to drive in rough water conditions.

Sorensen makes a really nice D Stock Hydro kit and it comes with a DVD with step by step directions.

http://www.boatracingr11.com/sorensenmain.htm

Is this helping?

Brad Walker

[Yellowjacket]

Brad left out one evolutionary step in the development of the hydro, and that is the cabover designs, of which the Ben Hur is one.

As speeds got faster the older shovel nosed hydros were blowing over. The logical next step was to move the driver forward and place him over the sponsons. These so called "cabover" designs were an interim step in that they didn't blow over as easily as a shovel nose boat, but they still had too much area under the hull and had more lift than was necessary, so as speeds continued to increase it was logical to start to reduce the area under the hull. The designers did that by cutting back the area between the sponsons and that's when the pickel fork designs were born.

A cabover has a three advantages that make it more suited to what you appear to want to do with it. The first is that the driver is set further forward and that leaves room for a passenger behind him. Secondly, this type of design has more lift and if you are going to carry another person in the boat you need more lifting area under the boat. Third, the added passenger is about at the center of gravity of the whole thing, so adding the weight there doesn't upset the trim as much.

Overall, if you have your heart set on a three point hydro, you probably are going to need to look at a cabover type design if you want to carry two people. The Ben Hur is 11 feet long and looks to be a bit short for a two person boat, but that's the kind of design you should be looking for. The downside is that if you make one much bigger than that it is going to be very flightly with just one person aboard. While you maybe could leagally race a hull like that, it isn't likely to be very competitive in comparison with the more modern picklefork deisgns of today. These are very specialized hulls that don't lend themselves to two place use.

All things considered, a modern tunnel hull is probably a better choice in that it can handle rougher water and is less weight sensitive. A cabover big enouth for two is going to be a flighty machine with one person in it, and if you build a smaller one, with two people in it is going to be running heavy. With a hydro there isn't as broad a load envelope as there is with a tunnel hull.

Hope this helps and gives you some more food for thought.

[mdaspit]

As speeds got faster the older shovel nosed hydros were blowing over. The logical next step was to move the driver forward and place him over the sponsons. These so called "cabover" designs were an interim step in that they didn't blow over as easily as a shovel nose boat, but they still had too much area under the hull and had more lift than was necessary, so as speeds continued to increase it was logical to start to reduce the area under the hull. The designers did that by cutting back the area between the sponsons and that's when the pickel fork designs were born.
.

Interesting, so did those old boats have lift built into the bottom also?
Or were they really a flat bottom? What about air traps?

My apology to the owner of this awesome photo. I found it on this site a couple years ago, and couldn't help but save it.

Think those guys could squeeze the throttle any harder?

[ZUL8TR]

hull design

[QUOTE=Yellowjacket;167211]Brad left out one evolutionary step in the development of the hydro, and that is the cabover designs, of which the Ben Hur is one. As speeds got faster the older shovel nosed hydros were blowing over. The logical next step was to move the driver forward and place him over the sponsons. These so called "cabover" designs were an interim step in that they didn't blow over as easily as a shovel nose boat, but they still had too much area under the hull and had more lift than was necessary, so as speeds continued to increase it was logical to start to reduce the area under the hull. The designers did that by cutting back the area between the sponsons and that's when the pickel fork designs were born...................................


--------------------------------------------------------------------------------------------------------------------------------------
Additionally as speeds increased there was a need to increase the afterplane length (back of sponson to rear planing edge)to reduce the angle of attack of the hull to the water and that coupled with the reduced area under the hull between the sponsons required (in most cases) to increase the length of the sponsons from their rear bottom edge to their tip thus further adding to the pickle fork look.

[ZUL8TR]

hull design

Interesting, so did those old boats have lift built into the bottom also?
Or were they really a flat bottom? What about air traps?

My apology to the owner of this awesome photo. I found it on this site a couple years ago, and couldn't help but save it.

Think those guys could squeeze the throttle any harder?

These older hydros generally had a flat bottom surface from rear edge to about 1/3 the length forward then the bottom curved upward somewhat to meet at the front to create the designed lift height at the bow to catch the air that went under the hull. There were some designs that had S curves built into the bottom. I think the Hal Kelly Ben Hur had this feature and his Jupiter B semi cabover hydro definately did. Air traps of various lengths were used. I raced a Kelly Wetback in the 1970's that used full length air traps. Each hull is different and requires testing to fine tune it.