Rigger "Rule of thumb"

[Tony Jacuzzi]

This is probably a well known fact (but I dont know it) I was wondering if there is a basic rule of thumb for balancing the weight on a rigger, or does it just not matter where the weight is positioned in boat. I have heard mention of strut weight etc. but really dont know much about it. Thanks tony J.

 

[John Finch]

Tony,

depends a lot on the boat and what you intend to do with it. SAW boats move the cg back so there is more weight on the prop to help keep it in the water. I use 3 to 4 pounds as a guideline on my gas rigger. With a 1/8th scale boat round nose you would want more weight at the front of the boat because they catch a lot of air under the hull, so the cg should be right behind the front sponson riding surface. With something like the 89 circus circus where the front of the boat is pickle forket a whole lot the cg is better moved back about 4 inches. So, there is less prop weight on the roundnose just because you want the weight forward, but it doesn't really matter because you are running a small x457 3 blade for example and it is fine with not a whole lot of weight to keep it in the water. What I don't like to do is add weight to a transom to get weight on the prop. I would rather move the front sponsons forward to put more weight at the transom. Imagine the boat as a teeter toter with the front sponsons being the pivot point. The more you move the pivot point forward the more weight goes to the transom. I havn't found weight distribution a big factor except at record trials where you are swinging big propellers on light boats.

The JAE is different as more weight is distributed to the transom because that design uses the rear shoe as a ride surface rather than the prop. If you try to use the prop as a ride surface with that boat you will have problems, so the engine is mounted mid ship and the sponson ride surface is way forward to keep the proper weight on the transom. I hope this helps.

John

 

[Chris Wood]

John while i understand what you are talking about. I would like to ask. Do you think and this is geared toward hydros.. It is more critical to have more cg to the back of the boat to keep the prop in the water.. or more on the front end to keep it from being light. Also.. is there such a thing as TO MUCH REARWARD CG or TO LIGHT OF REARWARD CG??

thanks

chris

 

[Jim Caldwell]

On Riggers, 30% on rear will get you in the ball park, JAE's 40 % on rear.

 

[Terry Keeley]

From what I've learned it's all about balance T.

If you're running X props that stay hooked up no matter what it doesn't really matter, start running 16's and up and more weight on the prop is your friend.

Also, forward and aft aero and hydro balance have way more effect than straight static balance, ie: sponson lift, rear sponson effects, rudder lift etc.

All that being said my heat boats balance around 25% of the afterplane.

 

[Tony Jacuzzi]

Its a RE gas rigger and it is wicked loose at 3.4 degrees AoA. I want to heat race it but that would be impossible at this time, its fast but has a poor running attitude for sure, I was really wondering if the rear exhaust and all the weight being directly behind the engine was throwing off the original engine location (built for SE.) because of the weight distribution I intend on lowering the AoA to 3.0 and see if I can still launch it but I have to mod the tub a bit etc.

 

[John Finch]

Its a RE gas rigger and it is wicked loose at 3.4 degrees AoA. I want to heat race it but that would be impossible at this time, its fast but has a poor running attitude for sure, I was really wondering if the rear exhaust and all the weight being directly behind the engine was throwing off the original engine location (built for SE.) because of the weight distribution I intend on lowering the AoA to 3.0 and see if I can still launch it but I have to mod the tub a bit etc.

If the engine is mounted rear of the front sponsons it is probably sponson dancing. Is that what it is doing?

 

[Terry Keeley]

Its a RE gas rigger and it is wicked loose at 3.4 degrees AoA. I want to heat race it but that would be impossible at this time, its fast but has a poor running attitude for sure, I was really wondering if the rear exhaust and all the weight being directly behind the engine was throwing off the original engine location (built for SE.) because of the weight distribution I intend on lowering the AoA to 3.0 and see if I can still launch it but I have to mod the tub a bit etc.

How deep is the strut? If you table the hull is the tub level? What prop(s) are you running?

 

[Charles Perdue]

One trick that I use on trying different AoA adjustments on the front sponsons is make a wedge (usually CF)that changes the AoA and stick it to the bottom of the sponson with double sided tape for a quick and simple adjustment. Once the optimum angle is found, then make that angle permanent.

Charles

 

[Tony Jacuzzi]

Its a RE gas rigger and it is wicked loose at 3.4 degrees AoA. I want to heat race it but that would be impossible at this time, its fast but has a poor running attitude for sure, I was really wondering if the rear exhaust and all the weight being directly behind the engine was throwing off the original engine location (built for SE.) because of the weight distribution I intend on lowering the AoA to 3.0 and see if I can still launch it but I have to mod the tub a bit etc.

How deep is the strut? If you table the hull is the tub level? What prop(s) are you running?

Terry the strut is even with the bottom of the rears and probably dead even no strut angle. Props I have been using are the ABC 2816, 2818 all the same series, and 1667 and H31's etc. I will measure the tub on the table with all sponsons on it to see if its level but I think it is.

 

[Tony Jacuzzi]

Its a RE gas rigger and it is wicked loose at 3.4 degrees AoA. I want to heat race it but that would be impossible at this time, its fast but has a poor running attitude for sure, I was really wondering if the rear exhaust and all the weight being directly behind the engine was throwing off the original engine location (built for SE.) because of the weight distribution I intend on lowering the AoA to 3.0 and see if I can still launch it but I have to mod the tub a bit etc.

If the engine is mounted rear of the front sponsons it is probably sponson dancing. Is that what it is doing?

Hi John the front of the engine is almost directly on the bottom rear edge of the fronts. Its riding with its butt down and the sponsons barely touching the water and pointing North

 

[John Finch]

Its a RE gas rigger and it is wicked loose at 3.4 degrees AoA. I want to heat race it but that would be impossible at this time, its fast but has a poor running attitude for sure, I was really wondering if the rear exhaust and all the weight being directly behind the engine was throwing off the original engine location (built for SE.) because of the weight distribution I intend on lowering the AoA to 3.0 and see if I can still launch it but I have to mod the tub a bit etc.

If the engine is mounted rear of the front sponsons it is probably sponson dancing. Is that what it is doing?

Hi John the front of the engine is almost directly on the bottom rear edge of the fronts. Its riding with its butt down and the sponsons barely touching the water and pointing North

Like Terry said......is the bottom of the boat parallel to the set up table? I use the 2918 prop on my rigger so I would think the 2818 would be fine. What is an RE gas rigger? What is SE? A picture may be helpful. Sorry for all the questions.....just trying to get some facts for a good evaluation Tony.

 

[dwilfong]

Tony I run a 2118 on my SGX2 and the boat likes this prop.

Start with putting the boat on a table with the turn fin removed. I use the thick glass table in the kitchen or the granite counter top.

Get a small digital level from sears real cheap like $35.

Set the level at zero on the surface then put it on the tub at a section that is flat in the center.

Now level the tub. after that put the level on top of the sponsons and see where the tops are at.

Thy should be close to level with the tips down just a tad say 1-1 1/2 deg. if not fix this first with shims under the tubes as needed.

Then go to the back and see how far the rears are off the table say .100 to start.

Then mess wit the strut as you run it. start with it level and touching the table.

Adjust up to loosen the boat then add some angle to the strut to bing it back tight.

Have fun testing.

David

 

[Terry Keeley]

Its a RE gas rigger and it is wicked loose at 3.4 degrees AoA. I want to heat race it but that would be impossible at this time, its fast but has a poor running attitude for sure, I was really wondering if the rear exhaust and all the weight being directly behind the engine was throwing off the original engine location (built for SE.) because of the weight distribution I intend on lowering the AoA to 3.0 and see if I can still launch it but I have to mod the tub a bit etc.

How deep is the strut? If you table the hull is the tub level? What prop(s) are you running?

Terry the strut is even with the bottom of the rears and probably dead even no strut angle. Props I have been using are the ABC 2816, 2818 all the same series, and 1667 and H31's etc. I will measure the tub on the table with all sponsons on it to see if its level but I think it is.

If the tub is level with all 4 points on the table (or 5 with the strut) you can deepen the strut a bit and even add a little angle (degree or 2). Running the strut lower than about 1/8" below the rears or running more than about 2* can cause other tho problems in my experience.

After that the only solution is to reduce lift on the front end by reducing the sponson AOA.

Are the sponsons adjustable? Are the rears? What hull is it?

 

[dwilfong]

The AOA of the bottom running surface is built in to the sponson. Hard to change. The top AOA will also change if you try to adjust this. the top means just as much if not more than the bottom. set the top then flip the boat over and check the bottom. with a digital level you can easily do this. the bottom is what it is. worry more about the top and where it is set if it dose not run good then remake the sponsons to change the bottom AOA.

Trying to adjust a bad bottom AOA will mess up the top AOA.

 

[Tony Jacuzzi]

Its a RE gas rigger and it is wicked loose at 3.4 degrees AoA. I want to heat race it but that would be impossible at this time, its fast but has a poor running attitude for sure, I was really wondering if the rear exhaust and all the weight being directly behind the engine was throwing off the original engine location (built for SE.) because of the weight distribution I intend on lowering the AoA to 3.0 and see if I can still launch it but I have to mod the tub a bit etc.

How deep is the strut? If you table the hull is the tub level? What prop(s) are you running?

Terry the strut is even with the bottom of the rears and probably dead even no strut angle. Props I have been using are the ABC 2816, 2818 all the same series, and 1667 and H31's etc. I will measure the tub on the table with all sponsons on it to see if its level but I think it is.

If the tub is level with all 4 points on the table (or 5 with the strut) you can deepen the strut a bit and even add a little angle (degree or 2). Running the strut lower than about 1/8" below the rears or running more than about 2* can cause other tho problems in my experience.

After that the only solution is to reduce lift on the front end by reducing the sponson AOA.

Are the sponsons adjustable? Are the rears? What hull is it?

terry the fronts and rears are adjustable (rears taped on the fronts have a boom block). Design wise it looks like one of Stu's boats, but it isn't.

 

[Tony Jacuzzi]

Its a RE gas rigger and it is wicked loose at 3.4 degrees AoA. I want to heat race it but that would be impossible at this time, its fast but has a poor running attitude for sure, I was really wondering if the rear exhaust and all the weight being directly behind the engine was throwing off the original engine location (built for SE.) because of the weight distribution I intend on lowering the AoA to 3.0 and see if I can still launch it but I have to mod the tub a bit etc.

If the engine is mounted rear of the front sponsons it is probably sponson dancing. Is that what it is doing?

Hi John the front of the engine is almost directly on the bottom rear edge of the fronts. Its riding with its butt down and the sponsons barely touching the water and pointing North

Like Terry said......is the bottom of the boat parallel to the set up table? I use the 2918 prop on my rigger so I would think the 2818 would be fine. What is an RE gas rigger? What is SE? A picture may be helpful. Sorry for all the questions.....just trying to get some facts for a good evaluation Tony.

hi John I appreciate all the input RE - Rear exhaust, SE Side exhaust

 

[Terry Keeley]

terry the fronts and rears are adjustable (rears taped on the fronts have a boom block). Design wise it looks like one of Stu's boats, but it isn't.

Sweeeet! You build that?

If it's all adjustable you should have enough "range" to get it.

I'd shim the fronts as high as possible (up to about 2.5* if you can), then table it. Set the strut flat on the table with the tub level, then attach the rears as "neutral" as possible (the angle in the pic looks good), set them on the table as well.

It'll prolly run best with a lifting prop like a 1667 or 14 series, a little cup helps keep them hooked up.

That should get you in the ballpark...

 

[Joe Warren]

This is probably a well known fact (but I dont know it) I was wondering if there is a basic rule of thumb for balancing the weight on a rigger, or does it just not matter where the weight is positioned in boat. I have heard mention of strut weight etc. but really dont know much about it. Thanks tony J.

Tony I have been thinking about buying one of the Super Long Euro Tuned quite pipes and just tig welding my boom tubes onto the pipe., And just hang a engine out front?? Dam those are some long pipes.

 

[John Finch]

Tony,

Terry probably has the right solution with AOA. If the bottom of the boat slopes up as it goes rearward you can't just measure the strut depth at the transom or you may be at a positive angle of attack. I have a boat that looks very similar and the bottom is flat, but it is actually sloped upward as it goes back from the front sponsons.

The only way to get the AOA right is to take off the turn fin, put the boat on a table, measure from the table to the bottom of the boat right where the trailing edge of the sponsons hit the table, then measure again about 6 inches rear of that measurement. Make sure they are the same measurement by putting a block under the transom. Now, go to the transom and look at the strut. it is most likely dangling in the air above the table. Bring it down to meet the table, measure the distance from the table to the underside of the transom.. Then, make the strut 1/8 inch deeper. Then loosen the strut enogh to make it moveable but snug, place a 3/8th block under the strut. set the angle of the strut flat on the block without changing the depth. Tighten the strut. Take out the block and rest the strut to the table. You will have a slight negative angle of attack and the strut height should be perfect for heat racing.

Terry.....while the 1667 is the best nitro prop ever, the low rpm of the gas engines work better with the 2916 and 2918 props. My gas rigger, probably the same design as Tony's runs 78 mph in heat racing trim with those two props. SE or RE should not be a problem when the boat is set up as described.

Let me know what you get on the measurements.

John