High Performance MPX Foil/Self-righting Trimaran-The Test Model

MPX Test Model

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Since I also bought the "RMGSwitch-BEC" , it appears that I'll be able to use the servo thats in the boat but I have to get confirmation on this. This neat little switch allows a 5 amp peak and 1 amp constant @ 6 volts. That should provide plenty of power for the high power servo. This is the servo thats now in the boat which it looks like I'll be able to use because of the switch: https://www.servocity.com/html/hs-5565mh_servo.html
This servo was originally purchased thru Tony Stillman at Radio South.
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Also, Rob emailed this morning that the "EH" style winch that I have gets 9.5 revolutions instead of the 6 of some other RMG winches-thats important for setting up the sheet(s). This may change but I'm looking at setting the mainsheet up at 2/1 so the travel of the continuous loop would need to be 37.89" and the movement of the main boom 18.9". The jib sheet will come off the same continuous loop-have to reduce movement of the jib sheet.
It will be tough to get that much travel.
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UPDATE- Just got word from Rob that since I'm using his switch I can use the HS5565MH that's already installed....

 

I have RMG winches in all my boats. You can get difference diameter drums to vary the amount of power and travel, though obviously you can also adjust the travel with your transmitter

 

MPX Test Model

Ian, I've used RMG winches for years. I had Rob make up special winch drums
with four or five winding paths for my spinnaker systems. I wouldn't use any other supplier!
Have you ever used his "RMGSwitch-BEC"?

 

MPX Test Model

This is pending Rob Guyatt's approval of the winch loading: (see update #1 and 2)
The sheets(main+jib) will be rigged off a continuous loop with 12" of travel.
For the main there will be a block on the mainsheet side of the continuous loop. One end of the mainsheet is attached along the rear crossarm to a loop
and with a bowsie for adjustment. Total travel of the end of the boom is 24"
and it will move from max out to max in(upwind) in 1.3 seconds.** Same with the jib except that it is rigged directly off the jib side(12" of travel) of the continuous loop to a small loop on the boom where it will be attached with a bowsie and a snap. Both sails @ max pressure produce a load of 25% of the stall torque of the winch in pressure of .44lb per sq.ft-the max with main and jib-more than that the rig will be reefed.
The aft end of the continuous loop will be rigged to the rear crossarm with a block attached to a line with a turnbuckle for maintaining continuous loop tension. When not being used the turnbuckle will be unhooked so as not to stretch the line while it's just being stored.
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Initially, the boat will have just the winch and the rudder servo operating off of 6V from a LiFE* battery (6.6v @2100MAH).

* LiFE -these are Lithium Iron Phosphate batteries and are much safer than the more common LiPo(Lithium Polymer) batteries. They also have a longer cycle and calender life. Like any multi-cell Lithium battery they require a special charger.
** The mainsheet will be lead to the boom from the boat fairly close to horizontally because more angle than this can cause excessive loading of the winch. This will require a more or less vertical carbon tube. So the mainsheet will NOT contribute to forestay tension. This could change a bit depending on what Rob says about the loading of the winch.
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UPDATE #1: Rob says that a load of 25% of the stall torque is not ideal but that all I need to do is watch and see if the winch starts to oscillate and if it does -shut it down. I may need to use a smaller drum but I like the speed of the 32mm(1.26") drum so I'm going with that initially. I can fairly simply change to a smaller drum if I have to.
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UPDATE #2: I've found a smaller drum that reduces the load on the winch to 15% of the stall torque(10% being ideal). But it does so at a cost of .8sec. of speed. So with the 25% drum, speed =1.3 seconds max out to max in(upwind). With the 15% drum ,speed is reduced to 2.1 seconds for the same movement. I want to go with the faster movement as long as I won't ruin the winch. Awaiting Robs word on this.......
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UPDATE #3: The decision is to go with the fast drum, keeping an eye open for any winch oscillation in max pressure conditions for the full rig-main + jib and/or main +Code Zero. A little oscillation won't hurt the winch. That means that the main and jib(or Code Zero) will go from max out to max in(upwind) in 1.3 seconds under load.

 

Finally managed to upload videos again. Latest action from Perth can be found here:
https://plus.google.com/b/104254705335138923320/104254705335138923320/posts

 

Mini 40

Moments of extraordinary performance-thanks for posting it Ian. What changes have you made since the first video? It was hard to judge performance compared to the other tri-how did they compare?

 

MPX Test Model

Something has been nagging at me since the test I made October 30th 2013(see #12 on the "What I expect" post above). The boat floated low at the stern-the water up to the top corners of the transom. Considering the boat sitting level (side to side) it's probably not too bad and, as I said in the "What I expect" post, the pitch up is not necessarily bad. On the F3 the pitch up was controllable by sliding the battery-big in those days. But the thing that nagged me was that the pitch up would be permanent on this boat-no adjustment. The freeboard at the stern was designed at 1/2" not much to start with and with this "pitch up" it was about 1/8th". With any heel and a turn the whole stern could go underwater-like the US1 I used to race if you turned while heeled even slightly.
So I was ready to install the sailwinch and hook everything up and I couldn't shake the feeling that something should be done about the stern sitting so low. No question it was my mistake for not building the damn boat lighter-I just didn't think it could go over 17 or 18 pounds-and it has at an estimated weight of 20lb.(original target weight 16.688lb) Even up to 22 pounds or so is not too much weight considering this originally started out as a scale model and the extra weight is only equivalent to one extra 175lb crew.(and at 22 add 66lb of beer , diet coke and ice!) And the sail area per pound is still equal to or better than the F3 (with the Code Zero)! The weight gain is due to the way I built the boat and the way I finished it-which added plenty of weight. My past history of one-offs is one of building too heavy-so I should have exercised more care. The sitting low by the stern is because I seriously under estimated the weight of the rudder and gantry- and built the rudder hydrofoil out of solid carbon and the rudder itself with a heavy core(to save time!). Well, thats the way it is--- the question was: what do about it-and if I was going to do something about it,it needed to be done now before the radio stuff was installed.
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The solution: In early March,(see post 1052) I gave the full size hull, on which the model is based, to my friend and sailmaker. I had decided before that if the foil system was tested fullsize it should be done on a boat designed from scratch for it. That freed me up to start thinking of ways I could make the model hull work better for pre-foiling and very light air. So what I decided to do was to change the hull shape to a lot rounder aft with flatter rocker and to lengthen it 5.25" which is as much as it can go with the current rudder system. That changes the L/B ratio from 5.7 to 6.2/1 which is an 8% improvement. And relative to the original waterline, about 3.5 lb. of buoyancy was added at a cost of less than 1lb in extra weight. I added the new shape directly to the old shape to save time. The skin is 1/32nd inch balsa covered with one layer of 5.8oz carbon. After carbonating the bottom I did the aft deck section with 1/16th" balsa carbonated with 5.8 oz. carbon. What filling there is will be done with "Super Fill"(from Aircraft Spruce) a very light epoxy based (non-shrinking) filler. Painting will be with Krylon this time around. Pictures of the whole job below(except filling and painting). It was a tough decision to make and took me a long time to be persuaded that this was the way to go right now but I completed the design and modification from the 27th-30th which was quite fast considering the circumstances. Cosmetics will be quick after the filler gets here Monday or Tuesday.
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Looks like we may get a break in the weather Monday or Tuesday so I may be able to fit the rig . I should be able to finish up the radio installation this week-and thats the last job before she's ready to sail.
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Summary:
--LOA of hull increased 5.25"from 60.75" to 66"(L/B ratio increased)
--buoyancy lowered, moved aft and increased by 3.5lb.
--freeboard of aft side of hull increased
--Weight increased less than 1 lb-probably right at 1 lb when cosmetics finished.
--Reason: to increase pre-foiling speed resulting in earlier takeoff.
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Pictures, L to R ,top to bottom. The whole sequence of the job is shown starting on the 27th and completed on the 30th.

 

MPX Test Model

I put the rig on the boat for the first time this morning-and as tall as it is it seemed to shrink on the boat-somehow it looked smaller.
The good news is that it fit perfectly at 4 degrees of rake. The bad news is that it has no tolerance for increased rake. Both the main and jib clew need to be cut higher to allow me to experiment with rake. The jib gaff is too long- hitting the mast-and the jib square top is too big for any increase in rake.
I called the sailmaker and he will do the work next Monday morning.

click once , expand, click again for best view----

 

Lookin good Doug.
Don't eat the toadstools.

 

Thanks Paddy!

 

I think I learned to sail on a boat smaller than this, holy s*&^ rigging and all puts it into perspective!

Also, I have had to cancel my plans to build a model so you will beat me there, apologies for the saying mine will sail faster, as I have just started building my house (so not all bad) though it means I will just go into full size build when I have the time to build it and have a mate of whom is doing a thesis on super-cavitation foils work with me on the foils, so maybe the full size version could be pretty interesting...

 

Looking good Doug. Now how did you resist floating it on that calm day 20m from the water?

 

MPX Test Model

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Thanks. Radio isn't in it yet. And while I'm close here access is really poor over a bunch of rocks, I'll sail it first off a beach. May do another float test shortly. And sail in a week or two...

 

Your getting there Doug, the trails and tribulations of building such a project.

 

MPX Test Model

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You're right about that, Warwick. Exciting times, though-that rig inspired me standing next to it on the boat. One of the condo residents(not a sailor) thought I was going to try and get on the thing and sail it! The original actual boat is "just" three times bigger-not that much when you think about it. Thanks for checking in-one of these days they'll be some sailing video!