Virtual wind tunnel testing.

[John Finch]

John,

It's interesting reading this thread on SAW boats as the stack of old Boat Modeler magazines I got from Joe Petro included your article on your and Kentley's efforts to brake 100 mph.

A few of the points I found interesting were you removing one rear sponson and finding you needed to get the engine on the pipe while turning on to the straight to keep the hull from blowing off.

Paul,

Making a SAW run can be difficult when you have to come up to speed with a super light boat with a lot of power and a small rudder. I think running SAW is more difficult than running ovals because of the transition from cornering and turning on the pipe as you set up for a SAW pass.

 

[John Finch]

Terry,

Maybe..less rocker LOWERS the transom to some as the boat runs. if the tub runs at any AOA then the air would speed up and cause a low pressure in the back.

Grim

Sorry Grim dude, not quite following ya there?

You may be right on the prop lifting more when the recurve is less. Like you said, it is a balancing act. I ran wedges under my sponsons so that a 3 degree angle of attack on the original sponson bottom turned out to be much more. I changed wedges for more or less angle and riding width. Lots of pond time. Found for turning the boat without a turn fin the width of the sponsons was very important. They had to dig in a bit so the rear of the boat would come around at slow speed. I have a whole file cabinet full of different width sponsons for SAW. Trent got smarter and built a set of sponsons where he attached different bottoms pretty easily.

Kentley gave you patterns for the SAW boat I took the 60 SAW record with before Martin took the record. Kentley built it for me as a payback for the first record boat he had that I scratch built for him. Think back....Remember E-city years ago. I thought he gave you templates for the boat.

No one I know of has had more pond time than you John, that's for sure! Have tried running w/o the fin but prefer a real small one, maybe I'll give that another shot. Could be just a bit better technique blipping the throttle to get it around the corner.

I remember it well, K Dawg just brought the template out, I never copied it. I did remember you guys running a 36" tub tho, mine was 30" at the time. Any guess how long my G2 and G3 tubs are?

36 inches? Hey, on cornering, try a wedge under the sponson but less width than the sponson so when the boat comes off plane the sponsons ride on the original sponson bottom but the wedge is under the water holding the sponsons like a turn fin. At top speed the wedge is on top of the water but for cornering it is in the water. Added photo up top of post and upside down but hey, just tilt your head left. LOL

John

 

[PaulHail]

John,

It's interesting reading this thread on SAW boats as the stack of old Boat Modeler magazines I got from Joe Petro included your article on your and Kentley's efforts to brake 100 mph.

A few of the points I found interesting were you removing one rear sponson and finding you needed to get the engine on the pipe while turning on to the straight to keep the hull from blowing off.

Paul,

Making a SAW run can be difficult when you have to come up to speed with a super light boat with a lot of power and a small rudder. I think running SAW is more difficult than running ovals because of the transition from cornering and turning on the pipe as you set up for a SAW pass.

Not surprising. When you think about it, our models have nearly 1hp/pound. Whether dealing with pavement or water, trying to get that amount of power down on a vehicle with such a high power to weight ratio is extremely difficult with models or full size vehicles.

Scaling factors come into play, but still a big challenge.

 

[Terry Keeley]

36 inches? Hey, on cornering, try a wedge under the sponson but less width than the sponson so when the boat comes off plane the sponsons ride on the original sponson bottom but the wedge is under the water holding the sponsons like a turn fin. At top speed the wedge is on top of the water but for cornering it is in the water. Added photo up top of post and upside down but hey, just tilt your head left. LOL

John

Lol, yup. Will give the wedge a try, makes total sense. With my regular 2" wide sponsons they just sink into the water in the corner and the boat starts hopping and usually dumps.

 

[DON MAHER]

Terry,

You said that your 2” wide sponsons would sink in the turns and dump the boat! May I ask how much does this boat weigh and is this gas or nitro? I would assume 2” would be gas sponsons? I had the same issue with my nitro rigger sinking and dumping in the turns until l widened the footprint 2”! Less leaverage to sink the sponsons in a turn. Also have you done any tests with the rear sponsons attached ln your simulations?

 

[Terry Keeley]

Terry,

You said that your 2” wide sponsons would sink in the turns and dump the boat! May I ask how much does this boat weigh and is this gas or nitro? I would assume 2” would be gas sponsons? I had the same issue with my nitro rigger sinking and dumping in the turns until l widened the footprint 2”! Less leaverage to sink the sponsons in a turn. Also have you done any tests with the rear sponsons attached ln your simulations?

Hey Don:

This was for my 67 SAW boat, here's a pic of the shorter (30") version with winglets and a ski:

Here's the G2 boat vs. G1:

Here's the fin I'm running:

G1 was 5 lb. 11 oz, the 30" version ended up heavy at 6 lb. 12 oz. I'm hoping this new one will be around 6 lb.

Didn't do any testing with other parts of the boat, was only interested what rocker would do...

 

[DON MAHER]

So you are using 2” wide front sponsons on the boat in the picture? That is an awful lot of drag for a 6.5lb. boat!

I ran 1” on my 7-3/4lb. 80 powered gear drive boat! Best pass was 122mph, with 10% overdrive!

 

[Hydro Junkie]

John,

It's interesting reading this thread on SAW boats as the stack of old Boat Modeler magazines I got from Joe Petro included your article on your and Kentley's efforts to brake 100 mph.

A few of the points I found interesting were you removing one rear sponson and finding you needed to get the engine on the pipe while turning on to the straight to keep the hull from blowing off.

Paul,

Making a SAW run can be difficult when you have to come up to speed with a super light boat with a lot of power and a small rudder. I think running SAW is more difficult than running ovals because of the transition from cornering and turning on the pipe as you set up for a SAW pass.

Not surprising. When you think about it, our models have nearly 1hp/pound. Whether dealing with pavement or water, trying to get that amount of power down on a vehicle with such a high power to weight ratio is extremely difficult with models or full size vehicles.

Scaling factors come into play, but still a big challenge.

Scaling can be an issue though my question has to do with something a bit more "full scale". What I'm curious about is, with the theoretical wind tunnel, since it doesn't take the water chop into account, how accurate of results can you really expect? I know the Miss Budweiser unlimited team used to take their latest boat designs up to the Bayliner plant in Arlington WA(about 90 minutes away) and run them through a similar program. From what I was told, the results they got were very rough though the team did do some "tweaking" to the boats during their construction based on the results of the computer testing

 

[Terry Keeley]

So you are using 2” wide front sponsons on the boat in the picture? That is an awful lot of drag for a 6.5lb. boat!

I ran 1” on my 7-3/4lb. 80 powered gear drive boat! Best pass was 122mph, with 10% overdrive!

You're probably right but I sure like the way it launches, just about drop it in the water. I'm hoping to lower the AOA if all this weight transfer and diffuser stuff works, I have molds for 3, 5 & 8* sponsons.

Got any pix of the gear drive? Was it home made or one of the Euro units? Running a gear in my 20 mono for years but its a 1.5:1 reduction.

Scaling can be an issue though my question has to do with something a bit more "full scale". What I'm curious about is, with the theoretical wind tunnel, since it doesn't take the water chop into account, how accurate of results can you really expect? I know the Miss Budweiser unlimited team used to take their latest boat designs up to the Bayliner plant in Arlington WA(about 90 minutes away) and run them through a similar program. From what I was told, the results they got were very rough though the team did do some "tweaking" to the boats during their construction based on the results of the computer testing

For SAW the water's pretty flat when you run so I don't think it would be an issue but in any case I think it just sorta points you in the right direction, the chit don't run in the lab!

 

[DON MAHER]

Terry,

My “Pet” geardrive sat on the bottom of Legg Lake for about 6 weeks after a stuff at around 110mph that snapped the tub in half!

The geardrive is a homemade unit that is like the Euro units, just heavier gears ( harden steel ) If you were to try the smaller wedges that John suggested you will see a diffident increase in speed!!!

 

[Terry Keeley]

Terry,

My “Pet” geardrive sat on the bottom of Legg Lake for about 6 weeks after a stuff at around 110mph that snapped the tub in half!

The geardrive is a homemade unit that is like the Euro units, just heavier gears ( harden steel ) If you were to try the smaller wedges that John suggested you will see a diffident increase in speed!!!

Bummer, good thing you got it back, I know the work involved in putting one of those together.

Wedged sponsons is on the list for the guys in the field.

 

[John Finch]

Terry,

My “Pet” geardrive sat on the bottom of Legg Lake for about 6 weeks after a stuff at around 110mph that snapped the tub in half!

The geardrive is a homemade unit that is like the Euro units, just heavier gears ( harden steel ) If you were to try the smaller wedges that John suggested you will see a diffident increase in speed!!!

Bummer, good thing you got it back, I know the work involved in putting one of those together.

Wedged sponsons is on the list for the guys in the field.

Terry,

I buy a pack of door shims at Lowes. They come in a pack of about a dozen shims and they are already wedge shape. You just put them on the sanding wheel to smooth them out and size them. Quick and easy.

John

 

[Terry Keeley]

Thanks, I'l have a look...