CG for Seaducer .21 SD3

[Doug Sick]

I put together a .21 Seaducer SD3 this summer but I'm have a big problem getting it un-stuck from the water. I know the built in hook in the bottom is designed to keep the hull in the water but what I have is way too far stuck. The hull contacts the water hard from about 4 inches back from the nose. I've put a 3 to 4 degrees of up angle on the strut to try to lift the nose but it does not totally fix the problem. The nose is so stuck that the back end wants to fish tail badly when the boat slows in the corners. It will hook very quickly if I hold the rudder steady in the corners. I have to pulse the rudder to keep the boat from hooking.

I did a temporary test on shifting the CG by strapping a 6 oz fuel tank to the top of the radio box. This moved the CG quite a bit and the nose came up to where I think it should be. However, the sloshing fuel was so high on the forward-aft CG that the boat got very unstable rocking back and forth and wouldn't stop till it rolled over.

I've seen the SD3's run well but only at near sea level. I'm working at 3700 ft here so we don't get the aerodyamic lift in hulls as at sealevel. I ran into a fellow at the Colorado Nats and he said he had the same problem with the hull, it was too stuck at their 5000 ft altitude.

I've built the boat according to plans but no CG is supplied. To move the CG back, I can build a custom tank and mount it under a revised radio box. I don't want to spend a lot of time doing that if that puts the CG back too far. I suppose I could correct a nose high attitude with ride plates but that would be departing quite a bit from the original design.

I shortened the rudder about 1/4 inch from the plans to allow the nose to ride up. It still had plenty of turn capablity still but I don't want to get too carried away as I think the boat is more sensitive to CG than the rudder length.

Your assistance would be greatly appreciated.

 

[M@MRacing]

Your best bet i would say contact Jerry at seaducer boats 954-493-7387 just leave a message for him he will get back to you

 

[john v]

jerry at seaducer wrote in about the same problem another guy had and it was the strut brackets were too low and the water was pushing up against them causing lift, use the search on iw and he shows the fix

 

[Andy Greene]

I put together a .21 Seaducer SD3 this summer but I'm have a big problem getting it un-stuck from the water. I know the built in hook in the bottom is designed to keep the hull in the water but what I have is way too far stuck. The hull contacts the water hard from about 4 inches back from the nose. I've put a 3 to 4 degrees of up angle on the strut to try to lift the nose but it does not totally fix the problem. The nose is so stuck that the back end wants to fish tail badly when the boat slows in the corners. It will hook very quickly if I hold the rudder steady in the corners. I have to pulse the rudder to keep the boat from hooking.

I did a temporary test on shifting the CG by strapping a 6 oz fuel tank to the top of the radio box. This moved the CG quite a bit and the nose came up to where I think it should be. However, the sloshing fuel was so high on the forward-aft CG that the boat got very unstable rocking back and forth and wouldn't stop till it rolled over.

I've seen the SD3's run well but only at near sea level. I'm working at 3700 ft here so we don't get the aerodyamic lift in hulls as at sealevel. I ran into a fellow at the Colorado Nats and he said he had the same problem with the hull, it was too stuck at their 5000 ft altitude.

I've built the boat according to plans but no CG is supplied. To move the CG back, I can build a custom tank and mount it under a revised radio box. I don't want to spend a lot of time doing that if that puts the CG back too far. I suppose I could correct a nose high attitude with ride plates but that would be departing quite a bit from the original design.

I shortened the rudder about 1/4 inch from the plans to allow the nose to ride up. It still had plenty of turn capablity still but I don't want to get too carried away as I think the boat is more sensitive to CG than the rudder length.

Your assistance would be greatly appreciated.

Okay, first off-

FORGET ABOUT cg on a Seaducer-

Period....

Set the boat up EXACTLY to the setup sheet Jerry provides .

Hardware/location/tank size ect......

Next we need to see (at least) a side picture of the strut / transom area of the boat to see where your at.

What prop ?? ect..

Im sure Jerry will chime in here when he gets a chance

Andy

 

[Tim_Duggan]

jerry at seaducer wrote in about the same problem another guy had and it was the strut brackets were too low and the water was pushing up against them causing lift, use the search on iw and he shows the fix

The thread is on page 2 in the mono forum. link

 

[ALLAN YUEN]

Important one key two things: set up measure 14.50" tank from inside of transon

11.25 to 11" engine's glow plug to inside of transon

better Rx hump 6V battery put end left into the radio box because run avoid right side

I had my experienced before SD3 20monos 29" and 33" Have a fun Good Luck!

 

[Doug Sick]

I finally got some pictures. The strut definitely tilts down to the water line and water off the keel could be pushing the back end up.

Two fixes, move the strut up or put a wedge between the strut and the hull to tilt it up. The latter will save me having to drill new holes.

I tried to run a 1440 three blade but the boat would bog badly. The one that seems to work is a 642 with some added pitch. The engine howls but it's not so fast.

 

[Bob Howard]

I would run a 438 or a 440. 1400 series props are lifting props which would add to your problem.

Bob

 

[Andy Greene]

I finally got some pictures. The strut definitely tilts down to the water line and water off the keel could be pushing the back end up.

Two fixes, move the strut up or put a wedge between the strut and the hull to tilt it up. The latter will save me having to drill new holes.

I tried to run a 1440 three blade but the boat would bog badly. The one that seems to work is a 642 with some added pitch. The engine howls but it's not so fast.

View attachment 15737View attachment 15735View attachment 15736

Maybe its just me , but that strut has a ton of positive pitch-

I would lower and level the strut and try the suggested props before I re-drilled anything....

Andy

 

[Duck899]

I would run a 438 or a 440. 1400 series props are lifting props which would add to your problem.

Bob

Bob, I think Doug meant to say....X-440/3

 

[Duck899]

I finally got some pictures. The strut definitely tilts down to the water line and water off the keel could be pushing the back end up.

Two fixes, move the strut up or put a wedge between the strut and the hull to tilt it up. The latter will save me having to drill new holes.

I tried to run a 1440 three blade but the boat would bog badly. The one that seems to work is a 642 with some added pitch. The engine howls but it's not so fast.

View attachment 15737View attachment 15735View attachment 15736

Maybe its just me , but that strut has a ton of positive pitch-

I would lower and level the strut and try the suggested props before I re-drilled anything....

Andy

From the picture with the ruler, it looks like the strut is neutral and up about 1/8" from the keel.....

 

[Shane Resiler]

If that strut bracket is perpendicular to the transom...and the rudde is parallel to the transom, there is something seriously wrong with the strut angle. It looks like the strut has positive pitch or the rudder is kicked in too far.....

either way, they look to be fighting each other....

 

[Rokieboater]

The seaducer has a very hard time working per set up instructions at that elevation. I bet your adjusted altitude is 5000-6000 feet. If you set it up exactly per Jerry's instructions and it does NOT work, there are things you can do to make the boat run very well at elevations. The 21 motor size just doesn't have the horsepower to overcome the stickiness of that hull at elevation. If you make sure the boat is set up per instruction and still are not happy with it I can help you out. The best prop at that elevation is an X-437/3 prop. The x440/3 is too big.

Let me know if you want to know what we do at our elevation

Robert Holland

Colorado--- 5200 feet high

 

[Rokieboater]

If that strut bracket is perpendicular to the transom...and the rudde is parallel to the transom, there is something seriously wrong with the strut angle. It looks like the strut has positive pitch or the rudder is kicked in too far.....

either way, they look to be fighting each other....

Or the transom isn't 90 degrees to the bottom......

 

[Andy Brown]

Doug,

Grind a taper on the front edge of the drive dog if you are using a collet to clamp the shaft.

The needed amount of gap between the strut and drive dog will allow water to hit the face of the dog...putting more down force on the hull. I'm sure that's not the main issue, but it will help, plus add speed. In fact if you are going to run the X437/3, a .312" O.D. dog would be the ticket.

 

[Andy Greene]

I finally got some pictures. The strut definitely tilts down to the water line and water off the keel could be pushing the back end up.

Two fixes, move the strut up or put a wedge between the strut and the hull to tilt it up. The latter will save me having to drill new holes.

I tried to run a 1440 three blade but the boat would bog badly. The one that seems to work is a 642 with some added pitch. The engine howls but it's not so fast.

View attachment 15737View attachment 15735View attachment 15736

Maybe its just me , but that strut has a ton of positive pitch-

I would lower and level the strut and try the suggested props before I re-drilled anything....

Andy

From the picture with the ruler, it looks like the strut is neutral and up about 1/8" from the keel.....

No way- Let me show you a pic of my X-Mono from the last race- If you think his is neutral -

your gonna swear I was NEG- and it was loose......

I have said it before- Its a very fine line on a Seaducer - esp a 20

 

[Andy Greene]

If that strut bracket is perpendicular to the transom...and the rudde is parallel to the transom, there is something seriously wrong with the strut angle. It looks like the strut has positive pitch or the rudder is kicked in too far.....

either way, they look to be fighting each other....

Both

 

[153stars]

As posted before.Jerry posted a pic" some guys boat that was having trouble" of cutting strut bracket at upward angle ,to prevent water from spraying up and hitting bottom edge. I have a sd3 that ran real tight did this it was SO MUCH better and it was way higher on the transom than this one. Directions say to mount as high on transom as you can with his hardware .His mount is smaller than most also. Now if I could get my sd2 21 to not ride completely out of the water I would be happy.Looks like weight is the more next option. It's a blast to drive by your self though.

 

[Doug Sick]

The picture with the ruler shows the bottom of the strut is just about parallel with the bottom of the boat. It looks like it has up angle but that's an optical illusion. The transom is angled back by 3 to 5 degrees (not perpendicular to the keel), probably so the boat comes out of the mold easily. I will have to either adjust the strut bracket by cutting the bottom edge to make it parallel to up angle or put a wedge between the hull and the bracket. I think I'll try the wedge.

I tried an X437 3 blade but I had to put a lot of pitch into the blade to get the boat to move. The X440 3 blade would not work. I'll pick up another 440 and try cutting it down bit by bit to find a point it will pull.

I suspect the altitude here is a bit of the problem as Robert Holland suggests. We are not as high as Colorado, only 3700 ft here in Calgary. However, it's enough to just take that edge off the engine power and the air density is reduced providing less aerodynamic hull lift. The hook maybe works at sealevel but possibly not here.

Thanks for all the assistance. I have the next six months to work on it not that the lake is frozen over.