Jump to content
Sign in to follow this  
Guest

Rob Denney at tthe clubnight

Recommended Posts

I went to Robs talk, and I have to say full credit for him to have the balls to talk to us when he kind of knew he'd get ripped..........

 

Ripped? That was about as "ripping" as being hit with a wet lettuce leaf. I assumed all the knockers had gone to the AC meeting and everybody at my talk was a big fan of low cost light weight proas. Next time don't be timid, introduce yourself.

 

two questions that need clarification please Rob.

 

I asked "whats a standard lamenate for a 50ft long proa hull?" you replied two layers of 450gram DB glass with some carbon unis running fore and aft.

 

I really wanted to know hoe you get the foam core into the hull after you "torture" the glass into shape, and then with horror realised you dont reinforce it? just 1mm of solid glass for the bottom of the hull with no core or inside laminate? please tell me im mistaken!!!!!!!!!!!11

 

You're mistaken!!!!!!!!!!!11 (is the drama really necessary?)

1) The 1/4 scale hull sample was 2 layers of 45, any more and it would have been hard to bend.

2) There is no torturing in the way that ply is tortured. Glass does not form compound curves the way ply does.

3) You are also confusing yourself by only thinking of it as a 50' proa. More important in terms of the laminate is that it weighs 700 kg all up, the hull is 400mm wide and it has minimal rigging loads, compared to what you are used to.

4) The hull has no carbon in it, just glass and foam.

 

Below the waterline, where the hull is curved into a semi circle, the laminate is 2 layers (6 under the mast) of overlapped 450 double bias, with 3 layers of 400 uni running lengthwise (about 3 mm thick), tapering to one layer of uni and 2 of overlapped double bias (about 2mm thick) at the ends. There are bulkheads at regular intervals. It is not as stiff as cored glass, but it is more damage resistant, and as the water applies an even load it is plenty stiff enough.

 

Suspend your "horror" that someone might dare to do something different and lay up a panel, bend it to a 400 diameter semi circle and put some bulkheads in it. Then a) immerse it and see if it deflects (it won't), B) jump on it and see if it breaks (it won't), B) drop a hammer on it from 5 metres and see if it dents (it won't) and c) clamp it as tight as you can with a g clamp and see if it delaminates (it won't). Then do the same with the foam cored parts of your boat, which is almost twice as heavy and half as long and has loads maybe 5 times as high on the hull skin from the rigging and traveller loads. Compare the results.

 

As I said, the core-less laminate in the floor would not work for a bigger diameter panel than this, but seems strong and stiff enough at this size. For bigger diameters, I include the foam and the outer skin, then add the inner skin after it is bent to shape. As I also said, the boat is an experiment to see how I can make lighter, faster, easier to build boats. Copying what everyone else does won't achieve this. If it doesn't work, I will beef it up, but so far it looks to be sufficient.

 

Other thing you said was a freedom rig costs the same as an alloy rig.

Are you saying that if an off the shelf alloy rig for my boat was 7K, a spar maker could build me a carbon "freedom" rig for the same kind of money? if thats what you think name the company who would do it.

 

As I said:

1) The boats I was referring to (the one in the video and an equivalent rm cat) have about 7 times the righting moment of yours and taller rigs. I am not sure how the comparison will scale to smaller rigs, but suspect badly for the one off rig.

2) It was 5 years ago, I'm not sure of the current state of play.

3) It was Australian prices. Getting mast prices for 8.5's from Halls or Southern is like getting blood from a stone, so no idea what I am comparing with in NZ.

4) The reference mast is glass and carbon, not carbon

5) It's a ballestron mast, not a freedom. The ballestron has more fittings and a carbon rcb sail track.

 

Let me know what you get for the $7k and I will do a rough comparison, although a single unstayed mast is not the answer for an 8.5 due to the height restriction. What I can tell you is that you could build an unstayed ballestron rig for your boat for a lot less than 7k in materials and a stayed carbon mast for less again. There is under $4,000 of materials in the 17m unstayed wing mast for my boat which has about the same rm as yours.

 

I may be able to supply you a stayed carbon mast for not much more than this, but won't know until the samples are finished. Let me know the alloy mast specs and suitable carbon mast specs and prices and I will see what can be done.

 

rob

Share this post


Link to post
Share on other sites
Other thing you said was a freedom rig costs the same as an alloy rig.

Are you saying that if an off the shelf alloy rig for my boat was 7K, a spar maker could build me a carbon "freedom" rig for the same kind of money? if thats what you think name the company who would do it.

 

 

"Freedom's just another word for nothing left to lose " Kris Kristofferson

Share this post


Link to post
Share on other sites

I was certainly impressed by the lateral thinking behnid the 8.5 proa. especially the idea of removing the racing hull and adding the cruising hull. However, the idea of 500kg of lead swinging around the place was a bit scary, not to mention possibly illegal? I have looked at the rule and wonder if a 350kg proa is 550kg underwweight, or is a 900kg proa with 550kg of lead swingin around the place? Anyone? Bill?

 

5/Weight

 

The minimum weight of the boat in race trim equipped to cat 5 including..

 

mast (s),boom(s), prod (s), all running and standing rigging, centerboards, rudders, engine, anchor and permanently attached equipment

 

But excluding... crew, consumables such as food, water and fuel shall be 900 Kg (for a boat at maximum length of 8.5m).

 

For boats shorther than 8.5m the formula for minimum weight in Kg is:

LOA (in metres) x100+50 = XXXkg

 

In the event that a boat is underweight corrector weights to bring the boat up to the minium weight shall be added to the boat divided equally between the two hulls in the following positions...

 

2m aft of the bow

2m fwd of the stern

Share this post


Link to post
Share on other sites

Sundreamers hull from the waterline down is solid kevlar and polyester resin, only about 4mm thick with bulkheads below the floor at about 1m centres. No foam at all below the waterline, just some foam stiffening in the flat side panels. Has never looked under threat.

Share this post


Link to post
Share on other sites
I was certainly impressed by the lateral thinking behnid the 8.5 proa. especially the idea of removing the racing hull and adding the cruising hull. However, the idea of 500kg of lead swinging around the place was a bit scary, not to mention possibly illegal? I have looked at the rule and wonder if a 350kg proa is 550kg underwweight, or is a 900kg proa with 550kg of lead swingin around the place? Anyone? Bill?

 

5/Weight

 

The minimum weight of the boat in race trim equipped to cat 5 including..

 

mast (s),boom(s), prod (s), all running and standing rigging, centerboards, rudders, engine, anchor and permanently attached equipment

 

But excluding... crew, consumables such as food, water and fuel shall be 900 Kg (for a boat at maximum length of 8.5m).

 

For boats shorther than 8.5m the formula for minimum weight in Kg is:

LOA (in metres) x100+50 = XXXkg

 

In the event that a boat is underweight corrector weights to bring the boat up to the minium weight shall be added to the boat divided equally between the two hulls in the following positions...

 

2m aft of the bow

2m fwd of the stern

 

If the boat is designed and built to the class weight, i.e it is supposed to have a 350kg floaty bit and 550kg of ballast, and it always sailed with the ballast as part of its usual sailing trim, it's probably within the bounds of the rule. This is provided the ballast doesnt swing outside the box, and the beam and length of the overll structure dont exceed the box limits, particularly diagonally. Your box cannot be a parallelogram.

Share this post


Link to post
Share on other sites

Clipper,

Ta. The lead would definitely be interesting and would be a challenge to optimise. If it wasn't legal, or when the class rules were changed to ban it, the next option would be to swap to a single beam and place the lead on a track on there. The single beam would be able to cant fore and aft. This is even more complex, lighter and less windage, but removes some of the cruising potential. It is not quite as good for maximising fore and aft righting moment, but theoretically would still result in a faster boat than a cat or tri.

 

Ballast is only one of the unexplored possibilities of the 8.5 rule, but one that is very suited to proas. It is inevitable that rules will have these possibilities and equally inevitable that, as the class matures, they will be exploited.

 

Phil, good to know I am following in the footsteps of a very smart guy. Pity I don't have his aesthetic sense.

 

Tim, pity you didn't come to the talk. Any chance of replying to my email to Sue (Hall spars office lady) with some prices of sections suitable for an 8.5 so I can get my article finished? Suspect this would be a better use of your time than posting old pop song lyrics.

 

Bill, Ta.

 

rob

Share this post


Link to post
Share on other sites

 

Tim, pity you didn't come to the talk. Any chance of replying to my email to Sue (Hall spars office lady) with some prices of sections suitable for an 8.5 so I can get my article finished? Suspect this would be a better use of your time than posting old pop song lyrics.

 

 

 

rob

 

Pity for who ?

 

Anybody who would like to know the price of a Hall Spar mast section for an 8.5 who is genuinely in the market for one is most welcome to call us up.

Quoting on a rig package is a time consuming process that for us begins with an engineering analysis of the boat we are quoting the rig for.

8.5's are not all the same and each requires a custom rig solution.

 

Good luck for your article.

Share this post


Link to post
Share on other sites
Guest

So if I understand what was said correctly, movable ballast is allowable ?

 

so I can build a light weight cat with water ballast tanks and pump the water to where ever I want to get the boat trimmed right and increase/decrease my righting moment.

As long as I carry enough water at all times to be at the 900kg minimum weight when racing as an 8.5 class cat.

Share this post


Link to post
Share on other sites

here we go, this will start a shitfight........

 

As far as I can see the word BALLAST doesn't even appear in the class rules.

Having the boat ballasted to a trim of 900kg and then moving the ballast to where you want it is fine, but if its water ballast then I think there could be an issue, particularly if you had the ability to scoop and release while you were sailing and thus the ability to alter your displacement. "oops we just let it go by mistake, an hour ago".

If there were no outlets I think it would be fine, you need to take all of your water all of the way around the course.

 

But if it all gets too hard there's this one....

10/ Eligibilty

Final decision on Class eligibility rests solely with the Open 8.5 Measurers and Class committee as established by the New Zealand Multihull Yacht Club.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
Sign in to follow this  

×
×
  • Create New...