No, I'm not talking about your Wife's undergarments, I'm wondering if there is any upwind, less drag, aerodynamic advantage to using a
lace up
the side type tramp, vs. the slide it into the hulls type.
The thought occured to me as I was going upwind on my old Prindle one day, in big wind. Now, my old Prindle tramp relly needs to be replaced, the side tabs that you tie into the hull slots are mostly pulled out, so about 6" of the sides of the tramp flap up in the air when I fly a hull and the wind gets under there...but it seemed as though it was much easier to control the boat's heal, as it did.
I started to wonder if maybe that's why the A cats (mostly) are using side lace ups? It allows the 'trapped' air pressure under the tramp a place to vent, which helps when the wind is up and you need to keep the hull only about 1' up? Or are they using them strictly to save a few oz. weight? Or something else?
OR...should we be designing our tramps to look like a wing laid on it's side, ie. fatter and round at the front beam (leading edge), with camber over the top, but flat on the bottom, tapered off to a thin trailing edge? Kind of like the Aka's on that 'flying' trimaran, Hydroptere? Do we want our tramps to help lift the boat, or no?
Seems the Curved Daggerboard school of thought says, lift the hull for less drag.
A tramp shaped like a wing would add lift too, right?
So, should we lace up, leaving an open slot on each side to allow the trapped pressure to escape, or use the lift to help get the hull up?
From my college Aero Engineering days, I remember that for any lift, there is also drag.
Without a wing shaped tramp, I think it's more drag than lift. But I'm going to have to get a new tramp for that old Prindle, I was thinking about a custom lace up vs. the same old thing.
I remember back when the I20 changed from the side slide to the lace up, but I thought that was due to isses of the slides pulling out of the hulls, more than any speed advantage. Did any of you who made the switch notice any improvements with the lace up?
Do you want lift from the tramp? Won't that force additional weight to counterbalance it (hiking)?
The side lace up tramps probably offer less wind resistance, due to an open space that allows the wind that gets under the tramp to pass through the boat when healing. I dont think that is the intent, I think the side lace up tramps were done more as a better way of attaching the tramp to the hulls.
Personally I've had lace up tramps on my first Acat and my HT. Both allow for me to really get the tramp tight, which stiffens up the boat and keeps your butt from dragging in the water.
A side benefit is that its a really nice place to put your heel and push yourself off the hull when you are trapping out. Thats the reason I like them laced up vs solid.
OK, here's another thought, take a look at the tramps on the AC or VX 40 cats. They use what looks like a big fishing net, about 3
square, open weave type tramp, vs. what we use on our beach cats, a much tighter weave.
Why? Does nobody make a huge roll of our tight weave? Or, is there 'less drag' with the open weave, where the wind can blow right through the entire tramp?
And why are no beach cats using it? I was seriously thinking about trying to buy a square of that 3
open weave stuff for my Prindle replacement, or something like they use for bow nets on a Corsair, or what they use on the bows of the big cruising cats, it would be very cool for my kids to just look straight down on the water rushing by. Like this: http:/
Yeah, it might hurt your butt more to sit on it, but hey, just sit on the hull and there won't be a problem.
Thanks Jack, did he use it for tramps or for fishing? The reason I ask is, the other place puts some UV protection on them, as they build them for cats in the sun.
square, open weave type tramp, vs. what we use on our beach cats, a much tighter weave.
Why? Does nobody make a huge roll of our tight weave? Or, is there 'less drag' with the open weave, where the wind can blow right through the entire tramp?
And why are no beach cats using it? I was seriously thinking about trying to buy a square of that 3
open weave stuff for my Prindle replacement, or something like they use for bow nets on a Corsair, or what they use on the bows of the big cruising cats, it would be very cool for my kids to just look straight down on the water rushing by. Like this: http:/
Yeah, it might hurt your butt more to sit on it, but hey, just sit on the hull and there won't be a problem.
I usually sail in shorts and that crap tears your knees to hell when tacking/gybing. One of our local sailing crew has it for a tramp on his Super 17 and he hates it.
Yeah, I was wondering about that part!
This stuff looks like it's a little smoother, with smaller openings, might not hurt so much.
http:/
Thanks!
square, open weave type tramp, vs. what we use on our beach cats, a much tighter weave.
Why? Does nobody make a huge roll of our tight weave? Or, is there 'less drag' with the open weave, where the wind can blow right through the entire tramp?
And why are no beach cats using it? I was seriously thinking about trying to buy a square of that 3
open weave stuff for my Prindle replacement, or something like they use for bow nets on a Corsair, or what they use on the bows of the big cruising cats, it would be very cool for my kids to just look straight down on the water rushing by. Like this: http:/
Yeah, it might hurt your butt more to sit on it, but hey, just sit on the hull and there won't be a problem.
I usually sail in shorts and that crap tears your knees to hell when tacking/gybing. One of our local sailing crew has it for a tramp on his Super 17 and he hates it.
I have the usual tramp in back and 2" net in the front. The front's not bad since I'm not usually up there when sailing. But when I'm working on something and have to kneel on the net for any period of time... wow is that stuff miserable. Also, there's no getting the net as tight as a regular tramp and keeping it there. You sink a lot deeper into it, which probably contributes to tearing up your knees.
I believe the reason for using the net tamps is that light boats with large tramps that extend beyond the main cross beam can flip over backwards when tacking in high winds if they use the standard weave tramps.
Do you want lift from the tramp? Won't that force additional weight to counterbalance it (hiking)?
Yeah, that's another issue, and that's why I've been wondering if we want vents or no vents, ie. lift or no lift.
And at first sight I thought the 'wings' on Hydroptere were wing shaped, but on closer examination, I guess they are not, and it flys anyway, on just the blades. Imagine if they built the aka's with a naca wing profile and could keep the top clean enough to generate even more lift!
http:/
His were for fishing. They make them out of various materials. I would guess that soccer nets are UV protected.
Based on my aerodynamic expirience, I would think that closed edges are far less dragy than laces. Also I think that the extra lift is something good, as it reduces the needed displacement. Finally it makes your main more efficient, not much, but a bit. All effects are certainly small, and if there are any benefits for a laced layout as better control in strong wind or faster trapezing, than go for it.
Cheers,
Klaus
some class rules also restrict size of openings in tramp.
Is this the beginning of an ekranoplan project?
Really? Which ones, and why? Is it seen as some type of speed advantage?
Really? Which ones, and why? Is it seen as some type of speed advantage?
F16 & F18 prohibit netting. I sure it is a combination of safety and minimizing cost escalation.
Tornado. 2mm. netting not allowed.
I guess your trap hook could get caught on it much easier than the standard tramp. I'm wondering if there is any cost difference though. I've got an estimate request in to that tramp co. I linked above, I'll see if it does cost any more than standard.
The ARC line uses netting. The ARC 21 uses a tighter weave than the ARC 30. Lighter weight and less windage.
FYI: a tramp is full of holes and does not need to bleed off pressure.
That's my vote. I've been told by a few over the road truckers the absolute worst thing to haul is the corrugated pipe. Not a lot of weight, but a ton of drag.
Even towing a beach cat, there's a whole mess of drag there, and not much weight. I've put 7 catamarans in a 4500# enclosed trailer and got 12.7mpg over the course of a 2500 mile road trip, I get only slightly better pulling a triple stack.
Our older ARC 22 (12' beam) has a three piece tramp with two sets of lacing, 1' inboard of, and parallel to the inner gunnels. Great for your heel, the hiking straps are right there as well.
I like it. We also have hiking straps 1' either side of centerline on the forward half of the tramp, so that crew can be secure forward and inboard in lighter air.
Dave
So the A cat lace up's are more for tightness than weight or wind resistance, and a fishnet type will hurt my knees and catch my trap hook, so stick with the standard Prindle set up and just keep replacing the tabs when they pull out...?
OK.
I guess if there were a better way, someone would have already figured it out!
To see how much air flows out the side laces attach some tell tales to the lacing and go sailing. I think you'll find pretty good flow.
Imagine what happens when a wave comes close to the rear beam at speed. There's a cushion of air that gets trapped under the tramp. It is drag. Vent that air and go faster.
You in fishnets is a very disturbing visual. And I doubt it's the fishnets that are hurting your knees.
Man, you walked right in to that....
I used to think, there must be a better tramp material, until I built a couple.
The best tramp material, for performance, I have seen is knitted polyester and looks like lace (see Sailrite, tramp material). It has big holes, it's light, and soft on the knees. The untreated version is good for 1 maybe 2 years, in the sun. The UV resistant version is good for 4-5 years, best guess. When this stuff fails, it fails fast. You go from,
I really should do something about this
to falling through into the water in a couple of weeks. I was lucky, mine failed while working on my boat. Friends tell me, it really sucks to sail home with no tramp.
The very best woven polypropylene tramp material works almost as well, is a little heavier, a little cheaper, and lasts 15-20 years in the sun. You can expect to re-stitch a tramp 1-3 times before the material breaks down.
Polypropylene net, you have already discussed.
Now, if you to try something new, once I saw a H16 whose tramp had been replaced with aluminum grating. The workmanship on that boat was way way below sh*ty but it had some advantages. If you could just solve the problem of it being a giant cheese grater, you are going to slide across.
cuben fiber. cause the chicks will think it's sexy. I've been told on numerous occasions this is the only reason that matters.
With regard to open nets as tramps I like to add my experience with this because I use an open net already for three year.
Never a
normal
tramp again for me; I like it and I love it. For me it is the right solution for coping better with incoming break and waves.
See for that
http:/
But you need to use the right open net!
No knotted fishing nets etc. They hurt on your knees.
I ordered mine with Sunrise Yacht Products (multihullnets.com) and they custom made for me from polyester rope with holes of 1-1/2
, treated for UV and finished with a rope border which I could lace very easy (lacing gap 2-1/2
) to the hulls and the beams.
Don't forget the net is WOVEN, not knotted.
In the trapeze you don't bother for the water which strikes through the net. I would say it enhances your feeling with the sea and your sailing!
Thanks for that, it is exactly what I was thinking about. I see by the video you have tied the front around the front beam, but I couldn't see how it is attached at the rear beam. Did you have a bolt rope there to slide into the rear beam, like most standard tramps? And on the side lacing, did you add anything special there or just lace it to the netting all the way up?
Also, what type of cat is that? It sort of looks like my Prindle 18 but the beam mounts at the front is different.
The front and rear beam are tied around with a through going line on the border of the net, just as you see on the front.
In the four corners of the tramp-surface there are RVS-eyes mounted on the beams which are the four basic strong attachments for the whole net. So the lacing only puts the net flat and gives the necessary tension for each hole of the net.
When mounted correctly, there is no difference in the tension and the awareness of
sacking
compared with a normal tramp.
The cat itself is completly designed and homemade by myself. The reason that you see a resemblance with your P18 is that the hulls are also asymmetric shaped just like all the prindles. To be honest I looked a lot to the prindle design; though I changed the volume-distribution.
With regard to the beams: for me it was the simplest and least weight costing method of fixing them permanently on the hulls.
Nice job on the boat build!
Now, at the rear beam, I guess you must have a raised traveler or some other way to lace the tramp to it? I couldn't wrap line around the rear beam as the traveler is built into it and it would restrict the movement of the car.
BUT...I could have a bolt rope on that end and just slide it into the beam as the normal tramps do, and tension it at the front with the wrap-around line like you have.