Hammerhead .21 Build

[RodneyPierce]

Hammer, I think the JAE ski is like 2* or something like that. How wide is that ski? I also believe that the wider the ski, the more it causes the prop to blow out in race water. I built my current rigger (untested until spring gets here) with a 7/8 wide ski. Im thinking this should help with the prop blow out when heat racing. Hoping so anyhow.

 

[Hammerhead]

Rodney,The AOA on the front sponsons is 3.1 degrees and the ski is 2.3 degrees. It turned out to be a little more than half a degree less, but I'm going to go with it. The ski is 15/16 wide. I need to get some of that black plastic that you used on your rigger for my next rigger. Next time I'm going to make my rudder spar and motor mounts out of it.

 

[RodneyPierce]

that should work just grand I would think!!!

 

[anthony_marquart]

I think too high a AOA on the ski will cause hop. I know from testing that too wide of a ski will also cause hop. I make my ski AOA at about 2 deg with steps or shingles. THis makes them long but I think it's good that way. A while back I was working on a "foot print" type of formula the would specify weight distribution between the sponon and the ski. It also contaned info on weight / surface area of the planing surfaces. I didn't get it finished or really finalized but I really do think there is a formula to a good running hydo. Before I'm done with this I will define a good surface area / weight ratio for both sponsons and skis. It would then be very easy to design a new boat and define the traits you are looking for in the hull. My latest attempt tried to let the sponsons lift if needed in chop but keep the prop hooked up,.. not have the ski bounce,.. but still have enough surface area to make the hull launch easily and lot lower in the turns.. I think it's just about right..

With "x" weight,. we should have "x%" on the sponsons and "x%" on the ski,... I would like to be able to define surface area also as in the trailing 1in of running surface should have "X" surface area per lb.. THis would also define the CG which is obviously key. I also think that sponsons and skis should taper front to back for the most lift an launch and less drag at plane,.. ...

All this is just my opinion,.. based about %60 on testing and %40 theory..

 

[Hammerhead]

Anthony, That would be nice to have a set rule for the most optimum AOA ratio between the ski and sponsons. It would be a nice thing to be able to reference, especially for the someone who has never built from there own design before. This would at least give them a drivable rigger. There are dozens of other variables some maybe insignificant, but do effect the total running characteristics of an outrigger, for example, prop, rudder, strut, sponson daihedral (if used), sponson and tub aerodynamics. I do make a lot of riggers. Some of them have been crap, but I think I have it down now. Most of my recent riggers have been for the most part, competitive.

I just got my Props-4-U props for this rigger. Thanks Mark! As always, beautiful work.

 

[Hammerhead]

I finished my turn fin. I made it out of 3/32 7075 aluminum. I also made my prop shaft bushing.

I used 7/32 brass tube with a piece of 1/4 brass tube soldered to the end for a stopper.

 

[Hammerhead]

After talking to Tim Leyde about making a 21 cowl for my rigger, I learned that he didn't actually have a mold for one, so I decided to make my own. Here are a few pics of the mold plug in progress. I have a pump for bagging, but I don't have the other attachments needed to make it work, so I think I will just lay this one up the conventional way for now. I will make the mold so I will be able to bag mold in the future.

 

[Hammerhead]

I made sure there were no negative angles, then I clear coated the plug for the 3rd time after sanding the 2 previous coats. I will sand it one more time to 320 then prime it. After that I will use proper release agents and then I will Gel Coat it, and lay it up with several layers of mat. I've never made a mold this small before. I wonder if it will need to be framed up for strength or will it be fine the way it is? Any inputs appreciated.

 

[Jim Caldwell]

If the hatch has no curve on the base it will be fine.

Be carefull of "green molds or plugs", not cured for a month. You must use PVA over the wax or it will stick, because the wax alone will not isolate the two epoxies.

I just used Freecoat FMA mold sealer(3 coats) and 770NC release(3 coats) on a 4 day old epoxy mold no problems.

 

[Hammerhead]

Great info Jim, Thanks!

 

[gil sonsino]

TR 104 mold release Hi Temp This is the product I've been using for years for my epoxy works.....some really big(full size boats).The PVA film is a must when used with epoxy compounds due to the chemistry of most epoxy hardeners that normally attack desmold waxes so I use to polish my molds then apply a primer followed by at least 5 or 6 coats of TR 104 and then apply PVA film .To get a luss finish with PVA apply it with a small piece of scothbrite (yellow side) ..you will be surprised how easy it is!

This a product from RD INTERNATIONAL you can easily find it in USA .I prefer the TR 104 high temp bacause it is more resistant than the TR 102 with the same results.

http://www.bottompaintstore.com/tr-104-mold-release-wax-14oz-can-p-10320.html

Hope this help

Gill

 

[Hammerhead]

I finished the plug. I will wait a few days to let the finish cure really well, then use some rubbing compound on it. I always do my plugs in black so I can see that I have a even coat of GEL coat. I don't have the capability to spray it on, so this makes brushing it on easier. I should be able to finish the mold by next week.

 

[Jim Mamaril]

Hey Marty, Looks good , I got something for you. I'll bring it with me sunday to the model expo.

 

[Hammerhead]

Wonder what it could be, Jim See you on Sunday!

 

[Hammerhead]

I pulled the mold off the plug this morning. It turned out better than I thought it would. After I clean the mold release film off, I will let it sit for a few days then try to make a cowl.

 

[Hammerhead]

Here is the final product. Not bad for an amature. Only a few spots where the Gel Coat was a little too thin, but it is definitely a usable cowl. I used a thin coat of Gel Coat, 1 layer of backing mat, and 1 layer of fine cloth. It turned out lighter than I thought.

 

[Hammerhead]

I have it ready to paint. I have test fitted everything, so it should go pretty quick from here on out.

I should definitely be ready to run at Twin Lakes with the NW Roostertails on the 10th of March. I'm getting pretty excited. Hope it runs as good as my .12

 

[Hammerhead]

All the graphics are on. Now all I need to do is clear coat it. Thank you Rick for the cool Hammerhead 21 graphics.

 

[Rick Sowell]

Looks good Marty, glad you like the graphics, I see you got them put on without too much effort. good luck and hope it runs great. Rick

 

[Hammerhead]

Yeah Rick, I bummed some transfer paper from the sign shop next door.

They clear coated really nice too. No runs! I have had problems with graphics running in the past. Not this time.