Trailerable Multihulls

Hello Phil,

Good to hear from you again...

The mast and beams are in cantilever in order to simulate the worst possible loads. For the beams...one hull completely out of the water while the other is buried beam on to a wave. For the mast, the possible pitchpole where the mast is buried in the water while the hull is in the air. I don't believe that the safety factors incorporated are excessive for the design...rated and cruiser.

The beams (4) will have to be super stiff because I have to ensure that kinks and binding are not a possibility, so their safety factors are additive with every extra beam.

The mast will weigh 5.846#'s per linear foot for a total of 204.61#'s. Are they over engineered? Yes, to cantilever. Is it required in my mind? Yes. Are they safe for full displacement? Yes and obviously super safe if sailed in light displacement. Can it be shaven a little bit? Probably down 1 size to the Z701, but it will be close and more wires will be needed. Do I think that a small Category B will need extra strength? Yes. Will it be difficult to fold? If my idea works for the system, the mast will have to be touched for two reasons...one, pull the pin, two, push it forward once it is horizontal so it sits on the deck. I say all of this readily admitting that my forte is not in the rigging and I trust the mathematics. I will of course revisit the calculations if it is shown that the mast is ridiculous for the maximum displacement in offshore conditions for a cruiser.

The mast will be raised and lowered with ease if the folding system I envision operates the way intend. Will I want to remove the mast for any reason whatsoever? No. All maintenance and inspection is executed while the mast is horizontal and stowed between the hulls.

I also hesitate to do so but I must. I have looked at several catamaran masts and have found them to be thicker on average than similar displacement trimarans and monohulls. I suspect that may be the case because catamarans will reach their maximum righting moments much sooner than the other designs and even when they haven't reached the maximum, they are still higher than the other designs.

I have seen masts that were wayyyy...smaller than I thought they should be and in many cases I feared for the crew secretly, but then I looked up and there was all kinds of wire attached to the damn thing. I suppose this is okay and sound engineering to reduce weight...for a racer. For a cruiser, I want to see the damn stick standing there when all the wires fail and I want that same mast to get me to the other side as I would for any other skipper.

Empirical data is great as is reverse engineering. This design brings forth several contradictions which will be tied to the Cat B rating. Comparing Cat B rated cruisers for the same displacement and purpose may produce results more favorable to the design. Remember that this design will have 2 wires outboard and aft and not 56 with a couple of intermediaries. It is a small vessel that will be rated to set to sea and everything will have to be stronger and many times bigger and heavier.

It is supposed to withstand F8 winds and 13.1' waves while it is small in Loa and light in displacement. That is why the rating is eeeeaaassssyyy for large vessels and a lot more difficult for smaller sisters. Have non rated vessels with lighter smaller mast and beams crossed? Yes. Was a significant risk taken? Absolutely.

Thanks
J

 

Hello Phil...

I have no delusions about my experience or knowledge in comparison to qualified accomplished designers. I consider current design trends carefully, but i am not always in agreement with them. Why? Well, IMHO, and I know that many will say "it is designed for its purpose", a large portion of many vessels are under engineered, even for their purpose.

Yes, I may forget something as have designers that update their plans because of a miscalculation or this or that. But my effort not to forget or overlook something will match or exceed the designers.

These events are always very sad and difficult for me to come to terms with. Look at the design and decide if there isn't enough vertical bulkheads reducing spans to less than 3' below the waterline for the length of the waterline and less than 6' for 1 section above the waterline. Then take a look at all the dedicated flotation and decide if this design is going to fill and sink.

You think that the scantlings on that vessel was good? Wait until you see the scantlings called out on the TR27B. I dare anyone to take a 20#sledgehammer to it...just remember to bring a lot of iced tea and ben gay for sore muscles.

Agreed and I will.

I'm not sure how to respond to this because I also am a fan of older designs. I would probably tend to agree, but in all reality, concepts have not stood at a standstill and tend to evolve. Sometimes they improve sometimes they don't.

Consider me a pioneer whom is not reckless by staying close to the accepted boundaries, but not afraid to explore a little bit beyond those boundaries. The reason my concept is considered "outside" the boundaries is because it is..."a Category B rated offshore catamaran that is trailerable. Let me rub a little and add "THE FIRST".


Thanks
J

 

Hello Richard...

I have a keen interest in completing as much of the design as possible to the best of my ability. I may have someone look it over, I may have them do the whole thing. I don't know, but I know I want to do as much as I can as best as I can and then measure against their opinion.

I see a different scenario and it goes like this.

Edited...because it may have been too harsh...Thank you very much Mr. N/A designer, but if I brought it this far and you cant make it work, then I will go somewhere else.

"Probably" didn't get the prom queen in bed on prom night. But, I am having fun. Perhaps, the math will be done by someone else if it needs to be done again.

To all...anybody have any specific comments on the mast and beams that demonstrate that they should be recalculated and called out again? I'm putting it all out here so that I can get "educated" if need be and will change anything "wrong" or "bad" for the design.

Thank's
J

 

Too much redundancy?

Gday JCD

I am pretty sure your mast will be real trial. You have to change the position of the CG of the mast by about 15ft. This means you have to lift the weight up this height at best. Rotating the mast will make the loads higher. 204 lbs (bare I would think) has to be lifted 15ft. That takes lots of energy. Unless you have a weighted cantilever system like Bolger's cat ketches you have to lift this up. Make model and check it out small scale.

As to the idea of cantilever redundancy - I have never seen this before. Most masts do really well and hardly any fail. I have broken more masts on in cantilever - Laser and Windsurfer-than with stays holding the thing up. Having stays and then engineering for cantilever will cost a huge penalty in weight. Better to spec up the rigging. A case in point.

My 14.1 metre mast has no diamonds but lowers and intermediates. When I take the mast off for maintenance I remove the lowers and intermediates - the thing wobbles a heap. I had to shimmy up the thing to fix a hiccup with the crane hitch and the stick moved under me heaps. It still had the caps on. To go cantilever you would have to go heaps more weight for no real benefit. With the wires my mast doesn't move - it is super solid. To design it not to fail without wires you should go to a proper freestanding mast - carbon or something like Rob Denney or Eric Sponberg can design.

About weight - Weight is a good and bad thing. Weight increases your stability but decreases performance and load capacity. Your boat will come up heavier than you design anyway - it always does. Even when exhaustively layed out on spreadsheets most designs float lower than the designers think they will. By increasing weight on too much redundancy you will restrict your cruising ability. Weight in a rig is a definite no-no. Go husky on the bottom where you will dry out on a shell or rock but seek the best advice to reduce weight aloft. Sail on a boat with a heavy stick and pitch and pitch. Weight out of the ends is the key.

I like redundancy - it is what reduces catastrophic failure to something acceptable. I would do it in a way that impacts less severely on the boat's usefulness.

cheers

Phil

 

Hi Phil
I was thinking of going with a freestanding wingmast. How does the weight compare to the same height conventional stayed mast? (about 30 ft).

Some people believe that freestanding masts are not worth the weight....but I imagine it would be if it's a wingmast.

 

Hi Richard

I have never sailed on a wingmasted cat - Dick Newick designed one in the eighties. It had a name like Tanui. It wasn't a success. Newick has done lots of free standing masts but prefers them in tris or proas. Tris and proas are much better at handling a free standing mast. They have a more gentle stability curve and they have much more bury for the mast. Cats are not well suited for free standing masts in the middle of the beam. They can do okay with one mast in each hull. A few Schionnings do this - the radical bay is one. They are not especially fast.

Putting a free standing mast on a cat would complicate the design a lot. Getting the thing to over rotate like a wing mast needs to would be very hard. Newick did domething like this for Pats - his own 50ft tri - but he really knew what he was doing and the idea did not take off on other boats.

Have you built or designed a boat before? If not, I would suggest not to go looking for trouble or conundrums. You will find plenty even if you go down the normal route. Stand on the shoulders of those who have gone before - or at least take into account the design ideas that 50 years of evolution has selected for us.

cheers

Phil Thompson

 

I'm certainly no expert, but Catsketcher and I have a fair bit of time on wingmasted small cats and dinghies, and in his case he's taken more than one championship win on them. It's noticeable to me (and him, I think) that the theoretical advantages of wingmasts (as calculated by some) do not seem to be achieved in real life, apart from their use on very high-performance multis and in some two-sail medium-speed non-trap dinghies.

This is not decrying wingmasts, but in the normal boat it seems that many other factors are more important than in the lift/drag of the whole package than a wingmast, and wings do come with problems. Our large-wing F16 type cat has an aerodynamically efficient wing, but to achieve that with light weight it has a very large and stiff section - so the mainsheet loading is extremely high which introduces further problems. Interestingly, in overpowering conditions in that class some top crews over-rotate, others under-rotate......everyone ignores perfect aero profile and finds better performance by worrying about gust response or other matters.

I once had the small wing mast in my dinghy jam the wrong way around. The loss of speed was, at a guess, aboout the same as if my crew had been hiking with their upper body at 40 degrees instead of 80 or so. Significant? In that race, yes it certainly was - these boats seem to be in one of the "sweet spots" for wings. But is the sort of advantage that would be worth too many other compromises?

As a skiff designer once said - if you have no mast limit, the weight put into a wing is better off increasing mast height.

 

Very interesting...thanks guys. I'm not interested in high performance windward ability...I guess this is where the wingmast would have it's biggest advantage.
For me, a stayed mast would be easier to raise and lower.
At this stage, it looks like a stayed mast is the better option.

 

Gday to you Phil...

Thanks for pointing out these observations.

I'm not sure what you mean by "trial", but I will take it to mean that it will be difficult to handle. You're probably right if the mast is to be handled all the time. I'm not sure why the mast has to be lifted to 15' or why the weight or CG has to have the same done? Can you elaborate some more?

I don't think I have seen Bolger's cantilever system, but I think that my idea is along those lines without the counter weights. I envision two bars hinged on deck running up the side of the mast to some point where it is pinned to the mast creating a pivot point. The mast step pins are pulled and the mast is folded aft (the step swings forward) to release the tension on the shrouds by way of sheets and winches. Once the mast is horizontal, the pins on the bars are released and the mast is swung forward and down to a set position which will hopefully be at a height just above the hulls. The bars are not structural and will only require that they hold up the mast weight and pivot/hinge smoothly. Outside of removing base pins, there will be no other reason to touch the mast. Is the description the same you imagine?

The beams and mast were designed in cantilever as an extreme and I know that their size and weight will be shaved down once the design approaches final lines. The beam will have stays so that weight can be reduced for the same strength once all the loads are traced. Your point is well taken and I do listen. Be patient...you will be more satisfied when this is done.

The beams will remain in cantilever as they are now, and they also will be shaved down because each and every beam is now calculated in cantilever for the maximum displacement and it would be unreasonable to think that one beam should be capable of supporting the design displacement when 4 beams can work to do the same. I will still make them a little stiffer than required, but that is because of the binding issues when sliding.

Again, the mast is calculated in cantilever to "see" what would be required for the greatest extreme strength. It will be shaved down to a good balance between stays and weight reduction. My forte is not in this and I want to start on the upper side and work down, but again, please realize that there will be no reason to manhadle the mast at all if the concept works as envisioned.

There is noooo question that Denney and Sponberg are the authorities to engage for a free-standing mast, but the design is not suitable for their masts.

I agree and will make every effort to design her as light to the waterline as possible understanding that the reality is always extra weight..

Spreadsheets are an excellent tool to "reduce" calculation times and they should be viewed as such. The only spreadsheet results that I would trust completely are the results which are based on accurate and factual data and not estimated or hypothesized information. I will definitely look to place any required weight as low as possible, especially for the mast and yes, I am strongly considering bearing area below the waterline for the possible beaching...hopefully not on rocks.

I like it too and believe it necessary if the definition for offshore is to be satisfied and like yourself, I will do it so that design usefulness is not impacted unfavorably, or as minimal as possible.

Right now I'm taking baby steps in this whole process because as already mentioned, it is not my forte. The design and all results are still very rough. The only true and completed progress made is the hull offsets. Those are final and everything else is subject to change until it is also final.

Update:

I have looked into the entire process for attaining the certification for the design and now understand why it may not have been feasible for accomplished designers to want to acquire it for such a small "low cost" design regarless of the assurances a skipper could be given or the safety designed for the rating. I liken the effort to an act of futility.

Every single calculation must be demonstrated and everything on the vessel must be approved and accepted. It is extremely discouraging with the number of requirements, applications, declarations and inspections required to attain the rating which are numerous and thorough. The work required for submission is encyclopedic and it appears the costs start to finish will be astronomical. If anyone thought the vessel design may have been difficult, they should now consider it a walk in the park compared to the administrative requirements. This could mean years.

I don't believe I have ever seen any "complete" plan that delivers the "full and complete" set of plans as required to be submitted...in my whole life or any past lives. I do not envy designers and tip my hat to them.

As of recent, I have engaged a qualified, knowlegeable partner that believes the design to have merit to assist with the plans and then build the "Demonstrator" scaled down to 18' LOA sometime this summer or fall so that tests can be made and data can be attained for finalizing or corrections to the plans. Hopefully, enough data will be recorded during the build to produce a comprehensive construction manual. Onward and upward!

Thanks
J

 

Mast Folding

Hello Phil,

I know that we keep coming back to the hardships that will be allegedly experienced in shipping the mast so, since I am having a hard time describing it, I did a very rough sketch on it and I am attaching it for all.

This is just the general idea and I haven't even begun to work on this at all let alone the geometry, so treat it as a visual only.

Thanks
J

 

Great news

 

Hello Richard...

Yes it is.

J

 

Mast will still be an issue

hello JCD

I think you will find the mast will still be tricky to raise. If you assume the mast is 10m long and 7kg/m (rough) then it weighs 70kg and has a CG 5 metres from the end. This equates to 350kgm torque to lift - if you rotate it around its base.

If the bars are 1 metre long then you are lifting 9m x 7 = 63 kg and the Cg is now 4 metres from the pivot so you need about 250kgm. In fact it is beter than this because you have the weight of the counter balance - 7kg x 1 metre = 7kgm - about 245kgm.

If you have the winch line lead from about 45 degrees from the mast as in the drawing you will need to increase the line loading to take into account the off axis pull - sin45 = .707 . = 347kg.

That is a lot of pull but that is what it takes to pull a big mast up. Of course increasing the lengh of the arms will reduce the loads. The arms will have to be stayed or A framed to stand upright.

Probably a bigger problem is that of folded stability. If the mast is up when the boat is folded then a tall heavy mast will compromise stability.

BTW - I just got back from camping. We took the little folder with us - the kids took her out on their own and the adults all had fun sailing around the lake. The idea of a trailerable cat is a sound one - its getting all the bits to work that is the bugbear.

cheers

Phil Thompson

 

Re mast raising - have you tried using another spar to act as a lever.

example at

http://www.macgregor26.com/mast_raising/mast_raising.htm

they use 'baby stays' to keep the mast in alignment during raising

 

Ahoy to all...Phil,

Agreed. I have to work out a way to make the raise less tricky. Those figures are close enough for general purposes and are definitely correct. I am going to try to call out a tapered mast to reduce weight aloft and lower the CG of the mast. Gotta work on it.

The bars are definitely going to be longer. I want to be able to fold up the mast and when I lay it down forward, I would like to get the masthead as close to the stem as possible. That means at least 2 meters. This should get me pretty close to the mast CG and really close if tapered.

The geometry has not been worked out yet. The geometry to fold the mast forward once it is horizontal may have to be worked out for a separate sheet because it may be difficult to pull back once it is laid down.

They will stand upright on their own because they are hinged to the deck and then pinned to 2 separate points on the mast, but yes, they will be stayed traversely when the bottom pivot pin is pulled for rotation so that she doesn't wobble in and out.

Once she is on the trailer she will be 17' wide and once she is folded, she will be 8.5' wide. Because the mast sits on one of the folding beam sleeves, the mast will have to be folded up before the boat is folded. This is an unexpected safety feature that just happened and was not planned. So the bottom line is that it would take great negligence to put her on her beam ends.

That's great. I'm very glad to hear that the whole family are avid catamaraners. I don't think there are enough trailerable catamarans out there for everyone. I am 100% sure that the trailerable concept is sound. I think it will be a very nice and easy design to set up or knockdown and definitely sail. As you have already pointed out getting everything to work is becoming more and more difficult.

Thanks again for the info...

J