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  #16  
Old 04-10-2017, 04:57 PM
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Thanks for that clarification Rob
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  #17  
Old 04-12-2017, 07:57 AM
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Oram cat builder here, it's a big no to polycore from me. A friend built a 40 ft cat from polycore and he won't do it again. It has its uses as rob said but i would go with Infused panels in pet foam. It is Foamed polyethylene plastic and has good compression but lacks a little in sheer, going to 110 kg3 gives similar properties to h80 and it is much cheaper. It is almost competitive with ply epoxy if you use vinylester for price per m2.
My friends cat needed to be reinforced several times with uni to stop the whole boat bending as he could not maintain rig tension, incidentally it was a mast aft head sail only rig Brian. Even with several extra layers of uni on the mast beam the rig tension could not be maintained and the boat kept flexing. Also the weight of polycore is much heavier than h80 foam. The quoted weights are usually without the scrim on each side and the extra laminate required to make it nearly as stiff as h80 defeat the purpose of using it in the first place in both cost and weight. Pet foam with grid score and perforations for infusion is the cheap option for the future I think, I'll be trying it out shortly and I'll post the results when I'm done. I am not using it for a boat, I know that's blasphemy / heresy / lunacy take your pick, I deserve to be banished, but it's still going to be an engineered composite monocoque structure so similar principals and loads etc.
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  #18  
Old 04-12-2017, 10:33 PM
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I assume you are referring to the vessel I linked to with the first posting of this subject thread?
Quote:
Originally Posted by b_rodwell View Post
I would be interested in what the Oram builders (and others) think of polycore as an alternative to joining duflex panels.

Here is a site of a the result of such an approach:
http://www.polycore.com.au/News--and--Events.php

and here is a site describing how it was done:
http://buildacatamaran.com/lyra1.html
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  #19  
Old 04-14-2017, 06:57 AM
sailhand sailhand is offline
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It could be Brian I'd rather not say. The boat has a new owner and i would not want to comment. Where are you based in thailand, I spend a lot of time in kanchanaburi.
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  #20  
Old 04-14-2017, 10:06 AM
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I'm living in Khon Kaen when I am there,.... but Florida most of the time

I visited Kanchanaburi about 2 years ago, preliminarily to look at a lot of the houseboats they have there.

Retirement Houseboat or Floating Home

Retirement Houseboat or Floating Home

http://www.boatdesign.net/forums/boat-design/retirement-houseboat-floating-home-23987-12.html#post692196
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  #21  
Old 04-15-2017, 03:22 AM
sailhand sailhand is offline
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We have a few friends in kon Kahn. My brother in laws brother Andy from australia and a pommy guy Dave and his thai wife detoy whom we met when we travelled through a couple of years ago. We spent a few nights at the aussie expat bar in town just down from the market.
we have a motorbike in kanchanaburi and will be moving there in the next couple of years. I have an oram cat to sell before we move. I am looking at a canal boat in Europe to get my water fix and northern hemisphere winter in south east asia somewhere.
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  #22  
Old 04-15-2017, 05:33 AM
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I have mentioned the aft mast polycore boat plenty of times as evidence of its lack of stiffness. I have been on the boat and the owner is a nice guy. Even when he had it up for sale he was very honest about the lack of stiffness and issues it caused. But then again correct engineering to begin with would have prevented the issue. The added weight and cost of other materials to keep it stiff would probably not be worth the hassle.

Sailhand this is the first I have heard of PET foam. Sounds promising and seems to have instantly made PET honeycomb redundant.

https://www.corelitecomposites.com/c...et%C2%AE2.html
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  #23  
Old 04-15-2017, 05:55 AM
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PET foam

https://www.corelitecomposites.com/f...ta%20Sheet.pdf

Vs PVC foam

https://www.corelitecomposites.com/f...ta%20Sheet.pdf

The 110kg PET shear strength is 1.32 mpa
The 80kg PVC shear strength is 1.13, 100kg is 1.49

So shear strength is lower, however the shear modulus (stiffness), the Achilles heel of the PET polycore is still quite low. Probably just a PET issue.

110kg PET 29mpa
80kg PVC 29mpa, 100kg PVC 37mpa

Compressive modulus is much higher for the PET though even though compressive strength is lower. Not exactly sure if that is good or bad when it comes to backing plate requirements. Still not sure if the benefits are there over plywood other than being able to say "no plywood".
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  #24  
Old 04-17-2017, 05:19 AM
sailhand sailhand is offline
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Hi Dennis hope your legs better, like I said the 110 kg pet is similar in properties to h80 pvc but much cheaper. I think the main problem with the polycore is the honeycomb structure the thicker the polycore the less sheer strength it has and it deforms easier. Used 6mm polycore in a lightweight dinghy a few years back and it still seems ok . The other plus for pet is that it's recycled pet bottles ground up and foamed so a good way to recycle all the empty soft drink bottles. Ian that used to own the polycore boat used to come and sit under our oram cat when we were doing our refit whilst he was building that boat. Ian is an engineer as far as I know and designed the boat from scratch. I helped him launch it and one of my mates did most of the build work on it and the subsequent refit. Like i said before it's a big no to polycore for me, pet might be OK it's my next little experiment for some road based fun.
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  #25  
Old 04-18-2017, 07:23 AM
rob denney rob denney is offline
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Quote:
Originally Posted by DennisRB View Post
PET foam

https://www.corelitecomposites.com/f...ta%20Sheet.pdf

Vs PVC foam

https://www.corelitecomposites.com/f...ta%20Sheet.pdf

The 110kg PET shear strength is 1.32 mpa
The 80kg PVC shear strength is 1.13, 100kg is 1.49

So shear strength is lower, however the shear modulus (stiffness), the Achilles heel of the PET polycore is still quite low. Probably just a PET issue.

110kg PET 29mpa
80kg PVC 29mpa, 100kg PVC 37mpa

Compressive modulus is much higher for the PET though even though compressive strength is lower. Not exactly sure if that is good or bad when it comes to backing plate requirements. Still not sure if the benefits are there over plywood other than being able to say "no plywood".
Sailhand, where are you getting your PET foam?

Dennis,
The benefits over ply are definitely there if you infuse the foam. Assume two 12m cats have 12mm core with stringers and frames to support it. (the foam one would probably have thicker core and less framing, but that complicates the arithmetic)

The foam boat would have 600 gsm glass inside and out, the ply one 200 outside, 3 coats epoxy inside. Assuming H80 foam, the infused foam weight per sq m is 2.8 kgs (1:2 resin glass ratio), the ply about 6.5 kgs assuming Okoume/gaboon ply at 16 kgs per 3 sqm sheet. If H100 foam was used, the weight goes up by 0.25 kgs.

The cost of the foam (H80, not sure about the H100) will be higher, but there will be less waste. It is less effort to cut and join foam and glass with knife, scissors and hot melt glue than cutting, scarpphing and carrying ply around the shop.

The labour involved in fitting out a ply boat is huge, up to 50% of the total. With Intelligent Infusion it is a smaller percentage of a smaller number.

Not building in ply is a good reason, but for a lot more reasons than low resale, rot and maintenance.

Are you back in Bris? Still got your drone? Bucket List has had a little set back (busted rudder mount), but should be ready for test sails and photos in a couple of weeks if you are still interested.
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  #26  
Old 04-19-2017, 04:42 AM
sailhand sailhand is offline
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Rob not sure where i will get my foam yet there are a few options available still looking at this stage. I have a house build to finish before i get to play with composites again unfortunately. I agree with you about ease of build and fit out with foam also much much less weight. Easy might not be so easy after all. Pricing at this stage is around 60-70% of pvc foam. Actually not that much different to the cost of good ply and the resin is cheaper. I won't be surprised if overall cost is lower with pet foam, this could be a game breaker for the ply lobby. Pete schwartzel from carbon works put me onto it. He is a great guy and very helpful. He is engineering my next project and so far has been fabulous to deal with. Bob oram recommended him and he was right, he did a free standing carbon rig for a 60 footer for bob a few years back.
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  #27  
Old 04-19-2017, 02:12 PM
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Quote:
Originally Posted by sailhand View Post
We have a motorbike in Kanchanaburi and will be moving there in the next couple of years. I have an oram cat to sell before we move. I am looking at a canal boat in Europe to get my water fix and northern hemisphere winter in south east Asia somewhere.
I assume you are going to look at a canal boat that already exist over in Europe?...there should be a pretty good selection of used ones on the market?

So you will spend the really hot Thai summer months in Europe, and the cooler winter months in Thailand?

Did you see those photos of the houseboat under construction on the waterfront there in Kanchanaburi?,...pretty quick and easy construction, ....and no land purchase necessary, which can be a real problem for foreigners in Thailand
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  #28  
Old 04-19-2017, 02:58 PM
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Polycore Boat's Stiffness

Quote:
Originally Posted by DennisRB View Post
I have mentioned the aft mast polycore boat plenty of times as evidence of its lack of stiffness. I have been on the boat and the owner is a nice guy. Even when he had it up for sale he was very honest about the lack of stiffness and issues it caused. But then again correct engineering to begin with would have prevented the issue. The added weight and cost of other materials to keep it stiff would probably not be worth the hassle.
Hi Dennis,
I would like to make note that it was NOT just the polycore construction that contributed to Lyra's lack of stiffness. I have addressed some of these issues in another forum discussion HERE
Quote:
Originally Posted by brian eiland View Post
I was just recently sent a link to this aft-mast article that appeared in an Australian publication called “The Coastal Passage”. Here is the PDF article (see pages 36,37) they made available on-line, but seeing as how the print size is very small (for us older guys), I've reproduced some of the 'rig related' portion of the article in a larger print style for this forum discussion.

I've included this material here as it is another aft-mast vessel that exist in real life, and that is the subject matter of this forum thread. The gentleman has some interesting observations about the sailing capabilities, particularly with reference to its basic single-sail configuration. I can't help but think that even his rig's capabilities could be improved with just a few modifications I'll outline in this posting. Meantime here is his observations:

By Ian Campbell, SC Lyra
I see quite a few cats using the “staysail sloop” rig now, and in a recent Multihull Magazine there were two new designs using a mainsail-less rig. Lyra has been in the water for a year and a half now and has 7000 miles under her keel including a Coral Sea crossing so we have had quite a lot of experience travelling without a mainsail and I think it may be time to give an honest evaluation of it.

The rig is not perfect; if it was every boat would have one. It does have a flaw that is inherent in the concept and it comes about this way. In order to get good balance the mast has to be stepped right aft and to have a rake aft. In order to get a similar sail area as a conventional rig the mast has to be higher. And the big staysails have to be made from heavier cloth. We wind up with a tall mast stepped far aft with two long foresails and with a short rigging base aft it is the very devil to get enough tension into the cap shrouds to stop luff sag. You wind on shroud tension until the hull starts to flex and still there is more sag than you would like.

Those two heavy sails on the sagging foresails flog from side to side in a big seaway so much that the masthead can sometimes flex forward as much as 5 inches. One reason for doing away with the mainsail was to get away from the annoying boom slatting to and fro – that drives me mad in a seaway, and here we have our own boomless equivalent. It's not dangerous or noisy, just annoying.

The cure is to rake the mast much further aft to open up the rigging angles at the masthead, and to build a stiffer glass beam athwartships under the mast compression post. From the point of view of performance I don't think this rig can be beaten for a cruising cat. The contention that the rig won't go to windward is codswallop. We travel at a hull speed equal to the true wind speed at 30 degrees apparent under auto pilot and down to 28 degrees hand steering, and the rig still pulls well down to 23 degrees when motor sailing.

Sailing against a Seawind in the Brisbane to Gladstone race we were pretty much neck and neck he was faster in light wind; we went better when the wind got up. We saw 18 knots a time or two, 12 a lot of the time though I must say we do a lot of traveling stooging along at 7 knots. We have done quite a lot of sailing in winds of 35 knots, gusting to 40 knots with seas to 4 meters and found the boat as rigged handles well with a few turns in the furler and no tendency to slide off a wave. No panic, no heart stopping moments. We only had a bit of water in the back of the cockpit twice from big breaking waves. In light winds the big outer staysail sits well and is always well balanced.

The true benefits are ease of sailing. Up wind in a narrow channel you just steer from side to side and let the self tacker do its thing while the other boats go by under motor, and downwind with the wind dead aft accidental jibes are a ho-hum event, the sail just goes to the other side. Whatever the angle of sailing If the wind gets too hard you just pull the furling line in on the electric winch and if the wind is light and variable it is no big deal to pull the other string and get a furled sail out. The result of all this is we sail a lot more than we did on any other boat I have owned.

The effect on the fuel bill is lovely. We spent a month traveling from Gladstone to Cairns and used 160 litres of diesel. We motored through the narrows and around the Hinchinbrook creeks to Ramsey Beach landing and through the channel in a dead calm. We used the engines to anchor and to maneuver into the marinas in Townsville and Cairns and we charged the batteries every two or three days. I don't think we could have done that journey over that length of time with a conventional rig and used so little fuel. We just would not have sailed that much.

So for the next boat definitely use the same rig, no contest. Rake the mast further aft and plan to move the shroud chain plates further aft. Spend some of the money saved in not having batten cars, boom, lazy jacks, sail covers, vangs, topping lifts, main halliards, main sheets, battens, reefing winches etc, etc, etc, on light weight headsails. Fatten the hull sections forward. Rake the bow a lot. Lift the run aft a couple of inches at station number 9. Design for a little more displacement...stiffen the main beam......build the bottom step at the transom higher............



Modifications (Brian would suggest)
I've hi-lighted those portions of his article that caught my attention, both positive and negative.

In general I have to believe that some improvements to his sail shapes would have to improve the wind propulsive efforts. After all the sail is acting like airfoil, and we all know the shape of an airfoils very important for its efficiency. Furling headsails, particularly “sagging” ones can produce awful sail shapes.

1) Modifying the leading edge of these foresails should be a high priority. Something as simple as providing a foam pad insert of varying dimension sewn into the luff of the headsail can flatten that partially furled sail needed for increased wind strengths. Here are relatively simply modifications to the leading edge of these roller furling/reefing headsails presented by noted designer Dick Newick back in 1980 (attached PDF patent).

2) Provide for a better backstaying arrangement. His angled backstays (the cap shrouds) is just not a very good means to provide for good forestay tensioning. He is placing all of the loads onto the windward side of the vessel, and asking this shroud to act as both a shroud and a backstay! Traditional shrouds on 3-point multihull rigs are already coping with big loads from the increased stability of the multihull form....now you want to add backstaying loads to that shroud....and ask it to operate at a much slimmer angle with masthead!!

I believe you have to get a little more creative about providing decent backstaying, that will in turn provide more acceptable forestay sagging, thus better sail shape.

One key to this better aft staying has to be looking at the situation somewhat analogous to what we already do with athwartships staying....the use of some spreader(s) arrangement. I call one of my 'aft spreaders' an 'aft jumper strut' . The arrangement I use on my forward leaning aftmast rig could also be adapted to a straight standing aftmast.

3) Another fault I find with the 'Lyra's Rig' is there appears to be a lack of a proper 'staying base structure' for the rig to attach to. Nothing is stayed back to the primary bulkhead that the mast sets on? There is no athwartships, nor longitudinal rigid frame structures to the vessel. It's an 'open cavern' vessel that depends upon its skins to support its rig....as such there must be a lot of sagging in the rigging as “the hull starts to flex” as he says. A little more attention needs to be paid to the 'hull structure' to properly engineer a boat for an aftmast arrangement.....in fact this could be said for a conventional rig on most multihulls as well.

On a positive note I did find these comments by the owner interesting....quote:
1) the contention that the rig won't go to weather is codswallop.
2) accidental jibes are a ho hum event.
3) the result of all of this is we sail a lot more than we did on any other boat I have owned.
4) I don't think we could have done that journey over that length of time with a conventional rig and used so little fuel. We just would not have sailed that much.

I re-emphase the fact that this vessel had very little, if any 'longitudinal stiffness helpers' such as the nacelle structure I specify on most all my cat designs.

If you look closely at how he attached his backstays/shrouds you will find them all attached to an aft step structure, and that structure can readily bend upwards via the flat deck 'plate' forming the aft deck floor.








Neither the backstays,... nor the shrouds are attached to any major bulkhead of the vessel.

On top of that look at the construction of any of the 'major bulkheads' of the vessel. Do you see anything that resembles an extra stiff/beefed-up bulkheads. I don't, ....all I see is a single this plate of sandwich construction glass/polycore material as utilized all over the vessel.







Summary: Way under engineered structure for this catamaran vessel and its higher tension rig requirements,.....not necessarily the fault of the polycore material.
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  #29  
Old 04-21-2017, 09:32 AM
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brian eiland brian eiland is offline
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Vessel Substructure to Support Rigging Loads

Just found an old posting of mine that relates to this 'stiffness' discussion.

Vessel Substructure to Support Rigging Loads
Sail Loading on Rig, Rig Loading on Vessel
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  #30  
Old 04-24-2017, 06:47 AM
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DennisRB DennisRB is offline
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Interesting posts Brian, but did you miss the part where I said "But then again correct engineering to begin with would have prevented the issue."
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