Doing some CAD work for the double ama/longboard setup. Just roughing it out for now so I can brainstorm on the connections I need to fabricate from the surfboard to the cross-member. I will likely do something similar to the windsurfing board main hull, with straps and non-destructive.
Stay tune for construction pictures of the new setup within a week or so! (working on some surfboard repairs ATM, pics of that coming too!)
After much thought, design, and consideration for my neighbors peace and quiet, I have taken the “easy” road and purchased two surfboards for use as pontoons for my windsurfmaran.
They are both almost exactly 9′ long. The blue one is a bit thicker/heavier than the yellow one, but it is okay. The yellow one is a BJ and the blue one is a McTavish Australian.
Both were really amazing boards back in their day. The BJ has been through hell and back and judging by the repairs on the McTavish, I think the entire board split in two and then was professionally repaired!
Similar to the method I used to attach the cross-member to the windsurfing board main hull, I will use a similar “no screw” method to attach the new ‘pontoons’ to the cross member. Speaking of cross members, I think I am 80% leaning towards using one cross member, but I still need to solve some weight distribution issues because much of my weight is on the rear of the windsurfmaran, which is only idea if I’m running or going full-speed. I don’t want to go around at 5 knots with my nose up in the air like an idiot.
At any rate, I will need to do a LOT of work on the yellow board to get it sea-worthy, and just a little cleaning mostly on the blue one, namely removing all the scuzzy wax from years of surfing.
I don’t surf much, but the blue board is fairly decent (repairs aside) and I’m really tempted to just go to the ocean and take a break from life, but the progress of the windsurfman takes priority over my own personal endeavors!
Working on some new designs for the windsurfmaran pontoons. Considering plywood (hollow) or using surfboards. Not going to do foam/fiberglass. Way too expensive, time consuming and awfully messy. It took me a month to get rid of most of the fiberglass in my apartment from last time…
At any rate, without further ado. The current contestants
1 – Full displacement, mounted at the center of the pontoon. Full width transom at rear. Square at 8″ x 8″ and about 84″ long.
2 – Semi-displacement, mounted at center of pontoon. Full width transom at rear. Square at 8″ x 8″ and about 84″ long.
3 – Double x-member design (WIP)
(picture coming soon)
My new flotation calculations. Going for a bit more than 35 lbs…
|Total Length (in)||72.00|
|Length of square midsection (in)||26.30|
|Length of remaining section(s) (in)||45.70|
|Length of nose and tail cone (in)||22.85|
|General form of nose profile Ax^2|
|A value (coefficient)||1.00|
|Form of equation||1.000|
|X-value given hull profile at y = 24||4.78|
|Total outrigger width||9.56|
|General form of Integral A/3 x^3|
|Form of integral||0.33|
|Value of integral from 0 to x-value (inches)||36.41|
|Area of half of nose cone rectangle (in^2)||109.23|
|Area of half of the nose cone (in^2)||72.82|
|Area of one nose cone (or tail cone) (in^2)||145.64|
|Area of both nose and tail cone (in^2)||291.27|
|Area of mid section (in^2)||251.44|
|Total cross section area (birds eye) (in^2)||542.71|
|Desired volume (ft^3)||3.00|
|Desired volume (in^3)||5184.00|
|Required height given volume (in)||9.55|
|Total weight of water displaced (lbs)||187.20|
|Total plywood surface area (in^2)||2460.92|
|Total cross section area of gusset plates (in^2)||277.07|
|Misc weight – glue/screws/paint (lbs)||10.00|
|Total volume of surface plywood||615.23|
|Total volume of gusset plates||173.17|
|Total plywood volume||788.40|
|Density of 1/4″ plywood (lbs/ft^3)||37.40|
|Density of plywood (lbs/in^3)||0.02|
|Total volume of lengthwise ribs (1/2 a 2″x2″)(in^3)||324.00|
|Density of ribs (doug fir) (lbs/ft^3)||32.00|
|Density of doug fir (lbs/in^3)||0.02|
|Total plywood weight (lbs)||17.06|
|Total gusset plate weight (lbs)||3.75|
|Total lengthwise rib weight (lbs)||6.00|
|Total weight of outrigger (lbs)||26.81|
|Total weight of water displaced (lbs)||187.20|
|Total flotation (lbs)||160.39|
|Flotation at 50% submerged (lbs)||80.19|
|Flotation at 75% submerged (lbs)||120.29|
|Flotation at 80% submerged (lbs)||128.31|
|Flotation at 90% submerged (lbs)||144.35|
Well, it happened. The windsurfmaran was “completed” and I went to the beach for my first sea trial on Tuesday July 18th at Cabrillo Beach, CA. Winds were forcast up to around 10 mph around 3pm. I arrived around 1pm.
It took me about 2 hours to set up the boat. I could go into the details, but I basically took everything off/out of the SUV, then put it all together. When you look at the picture it will be more clear steps I took in the assembly.
The wind decided to pick up, or perhaps Google weather was never as accurate as it could have been, but later reviews of the data indicated wind speeds above 15 mph.
To explain why the launch failed, I will briefly try to describe the circus that was my launch attempt.
The boat went well enough into the water, but I had one step before I could push off into the wild blue harbor, add the rudder. Only one problem, the rudder is at the back of the boat. She points nicely into the wind, but not when you’re at the back of the boat. Yes I had rope in the car. No I did not go get it so that my beach friends could help me launch. Hindsight something something…
So in a brief moment of genius, I decide to hell with the wind, I’ll just spin her around, aft pointing towards the wind and just get the rudder on (don’t ask how, missing both bolts somehow…) and then shove off pointed in the right direction. There is where calamity ensued. Apparently the force on the outrigger in 15+ mph winds is about 80+ lbs. I should know because I tried to hold up on up during some gusts, and suffice it to say, the 35 lbs I calculated for buoyancy required for the outrigger wasn’t nearly sufficient. So over she goes, plunging the leeward outrigger deep into the 30″ inch water, whereby she starts plowing into the sand and twisting up the frame…
A bit dismayed but not discouraged, I tried to straighten the frame up a bit, and then launch a few more times. The time was approaching 4pm and the wind just wouldn’t relent. During the ifnal attempt to hold the boat and put on the rudder, she swung around, buried another outrigger and just snapped off entirely at the office-chair arm rest joint, right at the bend. So at that point, it was clear the day was over and I had to bring everything ashore. I was pretty upset about the failures of the structures and at myself for being a bit foolish in a couple areas of the design. But at the same time, I needed to get in the field to get a sense of if the entire thing would go together or if I was just a crazy guy making drawings on notebook paper.
Well, I don’t think I’m crazy, but I’m certainly not a master sailboat designer. The main problem, as mentioned, was the lacking buoyancy on the outriggers, followed by the strength of the crossbeam/outrigger connection, with the third biggest problem being the seat post that snapped at the top. Other than those major failures, the rest of the boat seemed to function well in the torrent of winds. I will say I am still very concerned about being too stern heavy, so I will be contemplating the following;
1)Adding a rear cross member to gain some buoyancy from the outriggers
2)Moving the mast and crossmember forward to put the center of weight more towards the middle of the board
3)Moving the seat forward a bit
4)Adding some buoyancy to the rear
5)Building larger outriggers (to be about 3 cubic feet, rather than the 1 cubic feet I had)
Thanks to a kind stranger, I will have some pictures of the tragic failure shortly, but until then, just imagine the calamity unfolding because it is funnier in your head than in my memory 😉
So here goes nothing. Time to go from concept to reality!