Ultralight .21 rigger

[anthony_marquart]

while I'm working on the redesign of my current .21 rigger..(limp noodle turn fin spar support) I'm also looking at an unltralight version of the .21 boat that I build. There was a thread a while back I think started by Marty or Tom that talked about how to build light hulls. I am working on one now and would like to recap what I remember and see if I can grab a suggestion or two.

Hull construction

1/32ply sides and top,

1/16 balsa doublers on the sides

1/16 ply bottoms, all running surfaces

1/8 ply bulkheads

1/4 triangle in the corners.

Thinned epoxy to seal the inside of the hull

outside, sand to 220-240 smooth and straight to 2 part clear coat.

Add color to sponsons if desired..

cut all fasteners to needed length only,

Drill weight reduction holes in all hardware if possible.

I'm going to whip this one out quickly,.. any other suggestions?

 

[misshydro]

while I'm working on the redesign of my current .21 rigger..(limp noodle turn fin spar support) I'm also looking at an unltralight version of the .21 boat that I build. There was a thread a while back I think started by Marty or Tom that talked about how to build light hulls. I am working on one now and would like to recap what I remember and see if I can grab a suggestion or two.

Hull construction

1/32ply sides and top,

1/16 balsa doublers on the sides

1/16 ply bottoms, all running surfaces

1/8 ply bulkheads

1/4 triangle in the corners.

Thinned epoxy to seal the inside of the hull

outside, sand to 220-240 smooth and straight to 2 part clear coat.

Add color to sponsons if desired..

cut all fasteners to needed length only,

Drill weight reduction holes in all hardware if possible.

I'm going to whip this one out quickly,.. any other suggestions?

I think your going at this all wrong. Do the tub sides and walls with 1/16 ply and the turn fin side of the right sponson 1/16 too. do the shins with 1/32 even the bottoms to with 1/32. the transon with 1/8 with 1/16 added to it or do it with 3/16 ply. Put one coat of epoxy and then put one coat of clear. Oh joe is going to do this with his twin.12 jae rigger. Try using 1/4 hollow or solid carbon fiber rods for your boom tubes. Joe is running 3/16 solid carbon fiber rods on his .12. also use alum instead of brass for inserts for your boom tubes and sponsons....Now if you really want to go exstream. Joe is going to try this..His friend told him to get 1/64 ply. Then on one side epoxy it and put tissue paper thin fiberglass cloth on it. place it on glass and put glass on top too. Place some weight on the glass. This will help push access epoxy out of it. After its dry then you cut your parts out and epoxy it together.. you'll have a light but strong rigger.

 

[misshydro]

Aluminium water line

thats if he runs water cool.but good point and I forgot to add that.

 

[anthony_marquart]

All my sponsons have Divynacell (spelling) cores, Laminated structures are stronger than straight ply (of course we all know that!). right sponson to have internal structure for turn fin securing boom tube,.

Alumminim and nylon fasteners,.. great info..

 

[TomMoorehouse]

The best I could figure out without going crazy was this. Use 1/8 light ply for tub sides (it was lighter than 1/16 ply) and for the radio box front bulkhead. No bulkhead in the front of the fuel tank, just foam, 1/64 ply if you feel you must skin it. if your mounting the turn fin to the tub side then the transom can be 1/16 ply with corner reinforcements. Jae style my sponson inner and outters were 1/8 light ply, with a white foam core with no glue. 1/32 ply tops and bottom epoxied on. Balsa tub nose. I hope mine is under 3lbs

this is the thread http://www.intlwaters.com/index.php?showtopic=43904&st=0

 

[moparbarn]

deft brand lacquer sanding sealer (available at lowe's) & 1 coat clear everywhere you don't seal with epoxy.

 

[misshydro]

deft brand lacquer sanding sealer (available at lowe's) & 1 coat clear everywhere you don't seal with epoxy.

Tom I cant believe that 1/8 light ply is lighter then 1/16? Joe said he'll make two sets of tubs sides one with 1/16 the other with 1/8 and put them on the scale to see which is lighter?

 

[TomMoorehouse]

mine was.... no corner reinforcement with the 1/8" light.... but you need them with the 1/16" Don't forget to put that on the scale....

 

[LarryConrad]

I don't understand all this obsession with boat weight. My goal this season is to improve my starts and ability to drive a smoooth tight line on the course. In heat racing, boat setup and driving ability win races. Whittling down lap times is more important than whittling down boat weight. It doesn't matter how fast or how light your boat is if you can't drive it.

 

[Kevin Krogness]

Larry we are just that talented that it comes to weight to go any faster!!!!!!!!!!!!!

 

[misshydro]

I don't understand all this obsession with boat weight. My goal this season is to improve my starts and ability to drive a smoooth tight line on the course. In heat racing, boat setup and driving ability win races. Whittling down lap times is more important than whittling down boat weight. It doesn't matter how fast or how light your boat is if you can't drive it.

Larry weight is a big factor if you want to be faster. My first JAE.12 wade at 2.75. My new light weight JAE.12 is at 2.25. Joes will be more lighter then mine. This is what his jae.12 empty hull weighs.

 

[Mark Bullard]

I have been building boats for a lot of years. I do all of my boats the same way. The sides are two 1/8 light ply glued with CA. The top and bottoms are 1/32 on the small boats and 1/16 on the twins. Bulkheads are the same as the sides. The transom is double 1/8 light ply inside the sides and a single piece CA to the back across the sides. This ties the back end together. On the radio box area I Ca a piece of 1/32 ply to the inside top. This is done before the bottom is put on. The openning for the lid is routered out to leave a tape flange around the box. A second piece 1/32 in CA in the same area and then it is routered out to leave a 1/8 step flange to hold a 1/32 carbon lid. I have used all kind of different foams for sponsons but here lately I have been using balsa. I core out the extra that I don't need. The inside plate is 1/8 light ply and all other skins are 1/32. Everthing is CA togethered. I then coat the parts with a good finishing epoxy wiping off the excess. When doing this the epoxy soaks into the joints and this locks the boat together. On the big boats I do use a little 1/2 oz fiberclass cloth in areas that need it. Epoxy the sponson tubes and threaded long inserts into the sponsons for boom tubes and turn fin mount. This is the strongest and lightest that I have found.

Theses two JAE 21's weighted only 4 lbs ready to run.

 

[Tim_Duggan]

carbon over divinycel for sponsons ( divinycell is lighter than blue foan and stronger)

Greg,

I just built a set of 21 rear sponsons a few days ago with divinycell / CA and they were actually heavier than the previous ones which where pink foam / epoxy. Definately stronger though - but whether I need strength in rear sponsons is debatable! Fronts - no question.

Another weight saving suggestion or two. Laminate balsa or foam with the thinnest ply you can get for bulkheads. Delrin engine mounts. LiFe rx pack. Carbon pushrods for solid linkages. Although, don't compromise tub rigidity too much in the quest for the light weight hull or it will be a difficult boat to fine tune.

 

[Mick J]

carbon over divinycel for sponsons ( divinycell is lighter than blue foan and stronger)

Greg,

I just built a set of 21 rear sponsons a few days ago with divinycell / CA and they were actually heavier than the previous ones which where pink foam / epoxy. Definately stronger though - but whether I need strength in rear sponsons is debatable! Fronts - no question.

Another weight saving suggestion or two. Laminate balsa or foam with the thinnest ply you can get for bulkheads. Delrin engine mounts. LiFe rx pack. Carbon pushrods for solid linkages. Although, don't compromise tub rigidity too much in the quest for the light weight hull or it will be a difficult boat to fine tune.

Funny you should mention that Tim. I have done similar earlier this year. I built a JAE 45 but for the tub sides and bulkheads (except transom) I used Divinycell Core at around 3.0mm thick with 0.4mm aircraft ply skins. Skins were vacuum bagged to the foam.

Boat is super light and very rigid. Alas, still haven't finished her off. Like most of the projects in my shed I get them built fine and they then come to a grinding halt come time to paint as I hate painting with a passion. Got six riggers and a gas sport hydro all at the same point as of now...................needing paint.

Oh well, luv the building anyway

Johno

 

[gooycheese]

Yes I would think going lighter is in some ways better.... I would also guess in most cases it would be weaker.... Better material can make it lighter but will cost more, most of the time. I myself am not really worried about the super low weights.... I don't think I have hit the full potential of the boats I race, they are on the heavy side and i figure they can go faster. Yes if you do start with a super light boat I guess you will maybe go faster.... but careful around those buoy's =)

 

[Marty Davis]

Aluminium water line

thats if he runs water cool.but good point and I forgot to add that.

Even better is to drill a small hole in the bulkhead and pull the water tubing through the hole being very snug. Will seal the tube super well and no splices then.

 

[mark voorhies]

I don't understand all this obsession with boat weight. My goal this season is to improve my starts and ability to drive a smoooth tight line on the course. In heat racing, boat setup and driving ability win races. Whittling down lap times is more important than whittling down boat weight. It doesn't matter how fast or how light your boat is if you can't drive it.

Larry, big 10-4 on that. 90% relies on start of race, lane 1.Get the start, Then drive the boat to finish! driver driver driver!

 

[Terry Keeley]

I don't understand all this obsession with boat weight. My goal this season is to improve my starts and ability to drive a smoooth tight line on the course. In heat racing, boat setup and driving ability win races. Whittling down lap times is more important than whittling down boat weight. It doesn't matter how fast or how light your boat is if you can't drive it.

Larry, big 10-4 on that. 90% relies on start of race, lane 1.Get the start, Then drive the boat to finish! driver driver driver!

What if you're not a very good driver?

 

[LarryConrad]

I don't understand all this obsession with boat weight. My goal this season is to improve my starts and ability to drive a smoooth tight line on the course. In heat racing, boat setup and driving ability win races. Whittling down lap times is more important than whittling down boat weight. It doesn't matter how fast or how light your boat is if you can't drive it.

Larry, big 10-4 on that. 90% relies on start of race, lane 1.Get the start, Then drive the boat to finish! driver driver driver!

What if you're not a very good driver?

Then it doesn't matter if the boat is heavy or light.