Strut depth/Angle - My Sport 20 is hopping around

[Racerdude]

Hi all -

I finished my Supersport 21 (from Phil thomas) about a month or so ago. Ran good for a week or two, then just started hopping and bouncing like crazy. Can't go near full throttle withour serious threat of flipping over. I know that at one point Phil posted the recommended strut depth setup on this site, but at the moment, the "search" feature on this site does not appear to be working properly, so I cannot find what Phil already wrote.

So:

1) What is the recommended strut depth/angle for a superport 21?

2) Is there a tool that can measure (exactly) the angle?

3) Any other ideas for setting this boat up better?

The prop should not be at fault as it is a CDM polished and balanced prop. Still, it could have gotten bent or something (nothing obviously wrong with it).

Thanks in advance!

Jay

 

[Mike Hughes]

First

Did you change anything on the boat? If not, what turn fin do you run? If it is curlled at the bottom, then did the fin get bump out of alignment?

Mike

 

[Racerdude]

Hi Mike -

I run the grim racer sport 20 turn fin. Th boat flipped in the water, and it was at that point that it started acting funny. It did not hit anything except the water, and in fact it came down right-side-up. I think that your theory that it could be the turn fin has merit. I will go double check the turn fin right now.

I'll let you know what I find!

Thanks

Jay

 

[Racerdude]

Hi Mike -

I checked it with level (level the bottom of the sponson, then check the level of the top of the turn fin), and it was just a bit out. I adjusted it (as I think the instructions say to do) so that the turn fin and the sponson are parallel to each other. Going to the pond right now to check it out.

Thanks again, Mike.

Jay

 

[Mike Hughes]

It does not take much to get that little of a boat out of whack. The curl on the fin should be parallel with the ride of the boat. If it is pushed forward, the fin will act like a hydrafoil and lift the right sponson out of the water. If it is back then it will suck the right sponson down into the water causing the boat to pull right. Either of which you don't want.

Mike

 

[P THOMAS]

Hi all -
I finished my Supersport 21 (from Phil thomas) about a month or so ago.  Ran good for a week or two, then just started hopping and bouncing like crazy.  Can't go near full throttle withour serious threat of flipping over.  I know that at one point Phil posted the recommended strut depth setup on this site, but at the moment, the "search" feature on this site does not appear to be working properly, so I cannot find what Phil already wrote.

So:

1)  What is the recommended strut depth/angle for a superport 21?

2)  Is there a tool that can measure (exactly) the angle?

3)  Any other ideas for setting this boat up better?

The prop should not be at fault as it is a CDM polished and balanced prop.  Still, it could have gotten bent or something (nothing obviously wrong with it).

Thanks in advance!

Jay

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the strut depth should be about 1 1/16 deep and almost flat I have my strut set with a bit of angle. (rear lower than front, maybe 1/16)

the gim fin is thin and can be bent easily. I run the Tyndall turn fin.

See the picture of the strut, there is another turn fin pattern there you could try to make.

what prop are you using???

 

[Watercadet]

He is using a AB X440/3

Hey Jay! Hope to see it running again soon!

 

[Racerdude]

Hi Phil -

Last time we talked I was running an octura 440/3. I switched to an X442 polished and balanced by Andy Brown. It was fast until that flip.

Tonight, I tried a lot of combinations, but couldn't get the boat to settle down. I switched to aanother X442 and it calmed down some, but still flipped.

I have ordered an new grimracer turn fin and a new CMD polished and balanced X442 prop.

I am now hoping the when I flipped the boat (I was doing 40+mph), I bent the prop nd the turn fin. I'll try the new stuff when it comes in.

Where can I find the recommended turn fin?

Thanks for the input!

Jay

 

[P THOMAS]

The info is in the setup sheets if you still have them?

VIRGINIA CRAFTSMAN turn fins

DICK TYNDALL 8151 SAWYER LANE MECHANICSVILLE, VA 23111

r/[email protected] PH 804-730-7865

Be sure the turn fin is aligned straight front to back use a straight edge on the inside of the fin it should look parallel to the ride pad edge. Bend the turn fin in some at the rear, about 1/8th inch from parallel and see how the boat runs.

 

[bzubee]

You might also check your rudder position make sure it isn't kicked back or forward or bent.

 

[Grimracer]

I can not imagine you bent the fin.. it might have moved on the mount but again.. bending that fin..... i highly doubt it.

We use the same thickness fin (larger Ninja Fin) on out sport 40 and have blown that off and not bent the fin.. 7075 just does not bend easily...

If you bent it it would be the first time i have heard of anybody bending one of the sport turn fins (heck Ninja fins too) in use...

I dunno...guess it would not hurt to check the fin anyway..

Grim

 

[Racerdude]

He is using a AB X440/3
Hey Jay! Hope to see it running again soon!

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Thanks Adam!

 

[Racerdude]

I can not imagine you bent the fin.. it might have moved on the mount but again.. bending that fin..... i highly doubt it.
We use the same thickness fin (larger Ninja Fin) on out sport 40 and have blown that off and not bent the fin.. 7075 just does not bend easily...

If you bent it it would be the first time i have heard of anybody bending one of the sport turn fins (heck Ninja fins too) in use...

I dunno...guess it would not hurt to check the fin anyway..

Grim

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Thanks Grim! I too doubt that the fin is bent. It seems like a pretty tough turn fin. I agree that something maybe misaligned or moved.

Thanks again!

Jay

 

[P THOMAS]

I can not imagine you bent the fin.. it might have moved on the mount but again.. bending that fin..... i highly doubt it.
We use the same thickness fin (larger Ninja Fin) on out sport 40 and have blown that off and not bent the fin.. 7075 just does not bend easily...

If you bent it it would be the first time i have heard of anybody bending one of the sport turn fins (heck Ninja fins too) in use...

I dunno...guess it would not hurt to check the fin anyway..

Grim

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Yes those turn fins wont bend easy. I had a Grim turn fin on another ssp21 and it has not shown any problems.

The way the fin is mounted on the ssp21 could allow it to bend at the top mounting holes if you do not use some washers on the mounting screws. If the boat hits something on the fin it will not pivot out of the way mounted with the two 6-32 screws.

The front screw could be replaced with a nylon screw and that would allow the turn fin to pivot when struck. But we have not seen a need for a breakaway screw, the hull mount is reinforced and we have hit bouys and sticks with no unrepairable damages.

PHIL T

 

[Racerdude]

Hi all -

Thanks for your comments!

Well, I went out for the better part of the afternoon with a good friend of mine today, and he noticed that the back end of the boat is MUCH heavier than it was a week ago. We can't imagine why, but its a fact. Nothing that we can see has changed. Perhaps something inside the hull moved.

We taped a couple of medium sixed wrenches to the sponsons, and all of a sudden, to boat ran right again. It certainly appears that something internal to the boat moved, causing the boat to get too light on the front end. Additional weight on the front seems to have made it drivable again.

Still, a far from optimal solution, but at least now we know it is not the turn fin or anything else bout the setup.

Thanks again for all of the comments!

Jay

 

[P THOMAS]

Well there isnt anything inside of the hull except a long block of foam for flotation and it doesn hve much wiggle room if it was loose.

Do you have some drain holes in the sponson tips or in the upper corners of the transom? water can get into the hull and it wouldnt take much to throw off the balance.

 

[Will Gallagher]

Phill,

where is the CG on your SS21 RTR without fuel??

Several weeks ago I checked the CG on Jay's boat and it was aproximatly 16 inches back from the sponson tips (with out fuel) now its almost 19 inches back. :blink: With weight taped to the knose, the CG was back at 16inches and the boat handeled better. Not great, but better. <_<

I have no idea what would have changed when the boat fliped?

I am not so sure that the Speed Master Mini rudder was the one to use. I am going to give Jay one of the regular 21 hydro rudders to try. This should provide much more down force on the nose.

WG

 

[Racerdude]

Hi Phil -

Thanks for the reply!

The boat does take on water, (salt water here in San Diego), and so I have a 1/4" hole on the far left side of the transom. This hole is plugged with a drain plug shown in the photo below.

http://www.rcuniverse.com/magazine/reviews.../underhood8.jpg

Still looking for theories on what changed inside the hull to move the CG 3 inches.

At what distance from the transom does your boat balance?

Thanks in advance Phil!

Jay

 

[P THOMAS]

Hi all -
I finished my Supersport 21 (from Phil thomas) about a month or so ago.  Ran good for a week or two, then just started hopping and bouncing like crazy.  Can't go near full throttle withour serious threat of flipping over.  I know that at one point Phil posted the recommended strut depth setup on this site, but at the moment, the "search" feature on this site does not appear to be working properly, so I cannot find what Phil already wrote.

So:

1)  What is the recommended strut depth/angle for a superport 21?

2)  Is there a tool that can measure (exactly) the angle?

3)  Any other ideas for setting this boat up better?

The prop should not be at fault as it is a CDM polished and balanced prop.  Still, it could have gotten bent or something (nothing obviously wrong with it).

Thanks in advance!

Jay

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Jay found that one of the foam flotation blocks shifted to the rear of the hull causing the hop. Small changes can affect these smaller boats more than we think.

PHIL T

 

[boaterbill]

If I amy give you a tip on drying out the hull after racing. Drill another hole in the right sponson, After the racing is over at home, remove both plugs, tip the boat up to let the water out, then put it back on it's stand, so it's flat. Go to Walmart buy an aquarium air pump around $10, use a 3/16 brass tube long enought to reach to the front of the boat, attach it to the air pump, insert the tube in one hole leave alone for a least a day, then put tube in opposite hole do the same. I do this with my Mutt works great. Bill

Hi Phil -
Thanks for the reply!

The boat does take on water, (salt water here in San Diego), and so I have a 1/4" hole on the far left side of the transom.  This hole is plugged with a drain plug shown in the photo below.

http://www.rcuniverse.com/magazine/reviews.../underhood8.jpg

Still looking for theories on what changed inside the hull to move the CG 3 inches.

At what distance from the transom does your boat balance?

Thanks in advance Phil!

Jay

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