Trailerable Multihulls

Texel Rating

Hello one and all,

I'm attaching a list that contains approximate Texel ratings for over 100 designs for comparison purposes between different vessels or even your own.

I wanted everyone to have it because my initial TR rating calculation for the TR27B was accurately close and it was claimed by a Richard Woods that it could not be right because it would be faster than other notable designs, specifically the Dragon Fly. Well, it looks like it was right and it is faster than most Dragon Fly's, well, at least on paper.

The TR27B has an upwind TR of 120.4 and a TR of 93.5 reaching in heavy displacement. In light displacement the upwind TR is 114.4 and 88.8 while reaching.

Remember now, the lower the TR the faster the vessel. Take a look at how slow some designs are compared to other LWL.

I know someone that will be glad to have this in their reference library if they don't have it already.

Thanks
J

 

Weta Rating

Hi J and All,

I used the attached easy calculator example spreadsheet to get an idea of the rating for my new Weta 4.4m trimaran. I had to make an estimate of the mainsail luff based on published mast length because I haven't gone out and measured this stuff myself.

Gives a TR of 123.66 - perhaps you want to add it to your list. That doesn't look too shabby by comparison for a 4.4m long trimaran and her performance on Jakarta Bay on the weekend would tend to confirm that. Some shots also attached for fun. They are taken from a 34 foot monohull doing her best

Cheers,
Andrew

 

Hello Andrew,

Welcome to the thread.

Wow...even after all this this time and over 20 pages it is still nice to know there are "new" contributors keeping the thread strong. Thanks.

There are those that secretely wish the moderator would just shut it down you know. I cannot for the life of me figure out why But onward and upward as they say.

Well, it isn't my list. I can't remember where I got it on the net, but I will look for it and maybe the updates can be submitted there. But just keep it and update it. Maybe start a new thread to see how long we can make the list?

Not shabby at all. Very nice.
Thanks
J

 

I had a quick look at your scantlings. I haven't used Durakore myself so cannot really comment. Also I was confused by the scantlings in bold.

Having said that, I was expecting a fairly balanced laminate. The bulkheads (12mm and 18mm) seem very thick and heavy.

I know you are planning to build a one off, but if you were going into production you'd want to reconsider the laminates. Actually cutting and positioning the cloth takes a long time so the fewer layers the better. And of course you'd get a better volume discount so both your materials cost as well as your labour costs will be reduced.

Also don't forget that an ocean cruisers life is much harder than a trailer sailer's. So scantlings should, for example, be tough enough to withstand grounding on coral and for being on the inside berth with a big heavy steel fishing boat on the outside of you (which is fact is probably the worst loadings one can put on a boat).

I am late in replying as I have just come back from sailing my Merlin Tucanu. In a race held in 15 knots wind and flat water we were first to finish. We were doing a steady 14-15 knots on the gps when two sail reaching. We went faster with the spi up but were then a bit too preoccupied to check speeds.

You will see the Merlin on the TY sheet at 111, about the same as the Dragonfly and F27, and indeed in reality they are all of similar speed.

You will also see my Wizard design at 140. You can see a youtube video on my website of the Wizard doing 13-15 knots.

If the TR27 figures are correct and if TY relates to real speed then you'd expect the TR27 to be doing speeds around 16-20 in the same conditions. I know the Merlin is a 25 year old design, and Wizard 15, and things have improved since then, but even so, that would be very impressive for a easily trailable cat with live aboard accommodation and load carrying hulls.

I was expecting to see the TR27B data on the TY spreadsheet, then we could easily compare everyone's data.

I don't understand the reference to offwind and upwind figures. Clearly 88 is not correct for a TR27B with spinnaker as that is the same as Twintig Plus (built and owned by a friend of mine), which is a 45ft ultra lightweight cat with a big wing mast. A Dragonfly 920 extreme (with spi) rates at 99

Maybe it's now time to build and sail the TR27B??? At the very least upload the latest data and sketches.

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Hello to one and all,

Richard. I hope all is well and I hope you had a great time leaving others in your wake!

What kept you away from DuraKore? Something I should know? The scantlings in bold, are the scantlings required for the design and the ones not in bold, are the scantlings I recommend because they are better in properties and texture for less fairing after vacuum bagging.

Do you mean 50% of the laminate in the interior and the same in the exterior as balanced? If yes, I chose to put more laminate (60% of total) on the outside which is where the strength is better served. What do you recommend?

What makes you say the bulkheads are too big? Did you calculate them based on the full displacement of the vessel (2.975 tons) and then also have to have the sliding mechanisms and cross beams attached to them also for a design load in cantilever to transfer those loads to the hulls? Two beams will be 12mm, the crash bulkhead will be 18mm and the aft firewall for the motor will be 25mm. Are you basing it on empirical data or the ISO requirement? What would you recommend?

Yes it is a one off. For every plan available to the purchasing skipper, it will also be a one off because they will be building it themselves. Production? Wow. Too far ahead yet but if it goes to that then I’ll look at it because the intent is to make the plans available to the builder willing to commit as much sweat equity as he decides to commit or to contract it out instead, of locking it into a manufacturer that will then make the finished product half as good as the skipper would and three times as expensive. It is nice to know however that you would consider the design a possibility for the type of numbers associated with production.

Cutting and positioning cloth will take as long as it takes as will all other parts of the design. I have called out 2 layers per side in every part of the areas as standard if my recommendation is not used. The hardest to cut and fit will be the first and then it can be used as a pattern and the others can be cut a little larger. Pan wet the first, install, wet the second, install, and vacuum bag it. Actually, hand lay up with a smooth plastic on the outside skin to squeegee will produce a very fair and well bonded hull, but the vacuum assures the bonding and will reduce some unnecessary epoxy weight. Any thoughts or recommendations?

Believe it or not, volume discounts do not apply to the weight of the glass but the number of yards you purchase. The design will not require extensive amounts and I’m sure good volume discounts can be had. If you buy in huge bulk, like from a manufacturer or something like that, then it is by the pound, but the design is too small for that. Any recommendation on the weights you would use that may meet the same criteria as a single layer?

I haven’t forgotten. I am not designing for an inshore trailable light design. I am designing at maximum displacement to meet the criteria for the CE rating as a category B. This is a maxi trailable capable of setting to sea. As you can see from the skins for the bottom of the hull the outside skin is 30oz (1018gsm) and the inside skin is 18.5oz (627gsm). My recommendations are a little higher still. If you like, I can calculate the skin thicknesses for you if it will give you an idea of whether it is capable of withstanding an impact with coral. I didn’t design it to have the Queen Mary pushing up against it and the skipper should just come out of his bunk and ask the offending skipper to move, or he can just move his own TR27B, but it is extremely strong and probably stronger than it should be if compared to the thin widths on other designs. I want to make sure the skipper has a strong long lasting design.

Yeah, I see. Those are not measured results and should be taken with a grain of salt unless you are absolutely certain of the TR. Those are more like for comparisons. I’m sure that those can change pretty quickly with even the slightest change in displacement or sail area. To me, those are just fun for “bragging” that’s all. I think that the TR27B will be closer to 120 light when all is said and done.

I have seen it. If the TR27B gets those speeds I will be very happy.

Yeah, from your mouth to GOD’s ears, but again I thank you for the wishful figures. Everything points to excellent light air performance and high velocity ratios due to reduced wetted area and easily driven hulls with a high SDR, but the reality will be found when the scaled Demonstrator is tested. I estimate her at 12 knots in 18 knots of wind just before having to reef and I suspect that is an excellent velocity ratio for a cruiser. I will try for more speed though.

Nope. Not until it is built and everything is final. All of those designs are real and built. Right now the TR27B is 114 light but that can change fast if I’m not careful.

For the TR27B, 114 is based on main and 120% jib for 460sq.ft (42.6sqm) and for reaching it is based on main and gennaker for 866sq.ft (80.5sqm) Perhaps they didn’t rate with the gennaker. The Gennaker will not attach with a pole. I can try with a spinnaker or drifter and let you know what the value will be if you like but the numbers are the numbers.

Maybe. Right now the scaled folding truss cuddy model (ingenious indeed) is being constructed to see how it works and the hull shape has gone through some changes and significant improvements. This is in the interest of providing an impeccable folding system and superior seaworthiness from the hull for the skipper.

The mast and stowing mechanism is being studied (both quite unique by the way) for the best possible section and geometry. Once those are worked out and the loads traced and scantlings are calculated, the 18 foot Demonstrator will be built while the final plans are drafted and all the applications are prepared for the governing bodies to make a ruling on the design. Once it is tested, changes will be incorporated into the final plans and it will be submitted. A consultancy for an NA or NE considered an expert on or highly familiar with ISO will be considered to be retained to review the design prior to final submission for the rating just in case. This has been taken to a whole different level of serious as you can see. “The envelope is being pushed in design sophistication”!

This will take some time and all aspects are being thought out very carefully. Even you by your own admission and with decades of experience would agree that the design alone would take hundreds of hours even without the extraordinary design concepts for sliding the hulls, mast section and mast stowing mechanism wouldn’t you? Then there is the whole complex process of designing for the rating.

Do not be discouraged however, as I will be providing more information and pictures as everything gets refined and finalized. I have no doubt that even you with your highest of standards will be impressed with the overall final design and I am hopeful that you will continue to assist and contribute to the design.

It is still my mission to advance the field a little bit by closing the gap that keeps skippers from confidently setting to sea if they want by having the vessel rated offshore right from the design stage and just as important, still be able to avoid all the associated water locked costs by taking her home every day if they choose to do so in a simple and cost effective package. This has turned out to be difficult work but if work was easy it would be called vacation right?

Thanks
J

 

Re bulkheads. I accept that they need to be that strong. I merely meant that I would have thought there was a lighter way to get the necessary strength.

I'm still puzzled by your TR numbers.

I put in 8.3m rated length, 2800Kg boat weight, a mainsail of 32sqm jib of 15sqm to give a rated SA of 42 on a 11.5m mast. All numbers you gave except the SA's so I guessed at the proportions - not that it makes a great deal of difference.

The TR I got is 138, which is where I'd expect a heavy 27ft boat to be. To get a TR of 111 you'd need to halve the displacement. Maybe you could halve the boat weight but you still won't have any carrying capacity, which is what you are after.

So slightly confused as to how you got your figures (and that is why giving them out would help.) Yes we all know/accept things change as designs develop. So no need to stay shy.

We also know that no boat is as light or as fast as the designer hopes.

My ex father-in-law, Nico Boon, developed the TR system so I know it well, and I think it is the best simple indicator of multihull performance. In comparison, the Bruce number has no length factor, as I indicated elsewhere yesterday, so gives meaningless results.

The attached spreadsheet should help. Maybe someone will insert some guesstimates for the new America's Cup boats so we can see who will win.

Best wishes

Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Thanks

Ta for the XL Richard. Where can I find a list of ratings and what is hull beam - waterline beam of one hull?

cheers

Phil Thompson

 

see JCD's message above

 

Darn

My inability to read had me remembering that Abraham Lincoln quote

"Better to not say anything and have them think you a fool that to open your mouth and confirm it"

cheers

Phil

 

Hello Richard...

There probably is a way. Foam, carbon etc. That would require too little for the cost and for such a small areas the weight penalty for the extra strength is small. Straight plywood with skins is without a doubt the best way to go. I thought about plywood for the whole hull but the Durakore excelled for the weight.

I see. You and I both know that it isn't 114, you by experience and me by calculation...but you're not going to let me have any fun by keeping you in suspense are you?

You didn't calculate to the light displacement and some things have changed a little bit which changed the figure again. It used to be 125.4, but that was reduced a little with some design changes. It may still go up a bit more or drop a bit more by the time it is all over. But you can't wait can you? You gotta know so you can make some comparisons don't you?

Okay. Here it is. According to the calculator...(drum roll maestro)... it is somewhere between 121.90 and 121.92 but she rounds off to 122. He he he. Remember now that if I happen to dump all my water by accident during the race and make everyone take a piss on the leewrd side, the TR will drop significantly.

I'm attaching the spread. I noticed that the spread actually reduced it a little bit from where I had it because I had used the "actual" crew weight to get a "true" Texel instead of the Texel based on the crew weight by calculation.

Okay, there it is, the un-official true TR for the TR27B. On a positive note it is in league with some very nice designs so I expect the inshore skipper is going to have a very nice time leaving designs in its rooster tail as you can see by the rating list.

Thanks
J

 

Why is your draft zero in the spreadsheet?

 

My father has a Dragonfly 920 Extreme, and I would be amazed if a homebuilt cruiser was anywhere near as fast. Great thread BTW.

 

Hello Champ,
Welcome and thanks for looking.

The design is for daggerboards so I left it out as the difference is small. The hull draft is 1.12 feet (0.34m) and the dagger draft will more than likely be approximately 4.5 feet (1.37m).

Thanks
J

 

Hello PI Design,

Welcome to the thread and thank you for looking and your kind words.

That is an extreme machine and beautiful design. I have always liked them but their high price per pound always deterred me from considering them. I think I would tend to agree with you opinion if in regard to the the TR27B because as you can see from the Texel list, the D920E is at 99.

However, I can't agree in reference to "homebuilt" because as you can see by the same list, that there are designs that carry smaller TR's than the D920E and if built at home, they would be considered faster.

Without hijacking my own thread and I know that my thinking about what I'm about to say is not exactly part of this thread, I want to discuss my thinking on Texel a little bit. A LITTLE BIT, so please keep your own thinking to less than a thesis because I don't want to stray too far from the thread.

I don't consider "higher" TR's a bad thing.

1.The skipper with a low TR is racing against the fleet and must work every little puff and lull if he is to be succesful at crossing the line first, where the skipper with the high TR is racing the clock and just needs to fill his canvas and keep it filled to maintain the max speed.
2. The skipper with the low TR will have a more uncomfortable and fatiguing ride always having his design at extreme performance while the skipper with the high TR will have a more comfortable ride by just making sure his sails are always drawing full force to maintain the accepted hull speed.
3. The skipper with the low TR will arrive first missing the "journey" and stress to death waiting for the last design to skoodle in for time calculations while the skipper with the high TR will enjoy the "journey" knowing fully well he won't be first to arrive.
4. The skipper with the high TR stands a greater chance of upsetting the fleet by taking first on corrected time and that chance increases more and more the higher the TR rating.
5. In higher states of sea and wind, the skipper with the low TR will crash into waves with sudden and abrupt increase or reductions in speed while the skipper with the high TR will be more steady because momentum will carry her through.

These are just some thoughts, not all inclusive, but as you can see high TR's should not really be viewed as "worse" than low TR's, they are just on the opposite side of the spectrum and carry their own rewards such as comfort and the opportunity to shock the fleet by corrected time. I think this would apply for an racer or cruiser.

Please feel free to contribute your own thinking but we should not make it a debate issue, just thoughts and observations. If it gets crazy...maybe another thread to study the pro's for both would be a good idea. Personally, I don't think there are any cons to either and the rating should not really be used to say one is faster or better than the other. I pointed out some pro's compared to the lower TR's.

Thanks
J

 

Hey J,

I have only read to this point, in a hurry but one comment I would make is that from an engineering perspective I think the whole structure is stronger if the laminates are balanced. I know that in light weight foam dinghies they often include a layer of fine Kevlar in the external skin just for the puncture resistance so maybe an external Kevlar laminate below the waterline, or some abrasive resistant material if that's your concern... just a thought. Prolly been addressed, will read more later.