Contender Help

[TimClark]

I know someone that wants to take a Contender, and add a 250 sq. ft. assy to it, and he pretty much wants to know how big of wings would be required on the boat to hold it down. Thanks.

Tim

The total upwind SA of the Contender is 118sq.ft. and beam is 4.8' so adding a 250 sq.ft. spin is a bit much but based on rudimentry calculations he'd probably need to add a minimumm of 2.5' racks plus a new mast. I wouldn't recommend it and if he goes ahead given the excessive cost of everything these days I'd have a naval architect or noted small boat designer look it over-that will save money and time.
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Check out the specs on the Musto Skiff:
LOA: 14.9'
Hull Beam: 4.4'
Beam with racks: 7.7'
Upwind SA: 126sq.ft.
Asy area:166.7 sq.ft.

[TimClark]

Thanks for the info, I was thinking that 250 was a little big. But for him, 2.5 foot racks wouldn't be that big, because he sails on a 18 ft Skiff. Also, I was just wondering how you came up with those calculations. Thanks.

Tim

Tim, I just did some educated guessing with some basic calcs. The Contender has a max beam of 4.8' so I took half that plus three feet to give an approx CG of the crew from the CL with the boat flat(5.4'). With a 160 lb. crew that comes to 864ft. lb.'s RM. Dividing the RM by the SA(118) gives a CE very roughly at around 7.32 ft. above the CLR(center of lateral resistance).
Usually when sizing SA for a small boat I use a wind pressure of 1lb. per sq. ft. to match the SA to the RM but in this case because I was looking at the boat with the asy up I assumed (guessed) at a wind pressure of .35lb.'s per sq.ft. Total SA of 250 +118 is 368 and multiplying that by .35 gives 128 pounds
pressure which I placed at the above determined 7.32 feet which gave an RM of 942ft. lb.s. Dividing that by the already established righting arm of 5.4 ' gives 174 lb.s which was close enough to my starting crew weight of 160 to go with for this very rough estimate.
Looks like when compared to the Musto this is in the ball park.....
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edit/CORRECTION: Tim, I goofed! I divided by 5.4 which is the NORMAL righting arm when I should have divided by 7.9 which is the NEW righting arm with 2.5' racks. The correct answer(119lbs) would have clued me in that I was off on the pressure. I found this by applying the same method to the Musto where the pressure comes out to .43lb.'s at max RM with both sails set at he upwind CE . For the Contender the exact pressure at the upwind CE with both sails set is .469 vs. the .35 I started with. Sorry about that! This is still an approximation but much closer to reality and it backs up the 2.5' wider racks....

[TimClark]

Thanks for the explanation, that helps out a lot for my own design endeavours.

P.S.-How is the foiler going?

Tim

Tim, thats just a rough method of answering your question in a hurry based on lots of experience; to learn to do it right you should consider a course like Westlawn or any of the others currently available.
The foiler is about to have surgery.....

[TimClark]

For the foiler surgery, are you hacking off some weight? What kind of surgery are you planning on?

Tim, note where the "rack" tubes go into the hull:
aeroskiff012.jpg
Address:http://www.monofoiler.com/images/aeroskiff012.jpg Changed:11:07 PM on Friday, October 31, 2003
That was a bad mistake because as narrow as the boat is when it rolls a little the two forward tubes hit the water. It is an annoying problem (that should NOT have happened) but will be remedied by cutting the tubes out of the boat and moving the inboard end up IF I can get the tubes out in one piece; otherwise they'll be moved inboard and up. In addition to that removable buoyancy pods,a wand with manual overide and an unstayed rig will be added that will be interchangeable with the current rig. Hope to have the boat going again in a couple of months or so.

[TimClark]

I see what you mean, after looking at those pic it does look like the rack could dig in pretty easily. What kind of material are you using for the hull? It looks like if you used a lighter construction with a little more freeboard you could have a generally similar rack set-up and not dig in. Good luck with the re-construction.

Tim

[CT 249]

Originally Posted by TimClark

I know someone that wants to take a Contender, and add a 250 sq. ft. assy to it, and he pretty much wants to know how big of wings would be required on the boat to hold it down. Thanks.

Tim

When world-class Contender sailor Jo Rosler moved from Germany to the US and started sailing on LIS, he added a metre to the rig, a fully-battened main and a roller-furling reacher. He also experimented with wings....the width is on another computer but looking at my pics I think they were about 3' wide. However, he found that they tended to drag (they don't angle up much) and made the cockpit too much of an obstacle course.

I have seen this done on Contenders modified for 2 crew, but just as a fun boat. Can't really see why you'd need a bigger mast if you are just adding an assy; Canoes for example switch to an assy by just adding another set of stays and spreaders to the topmast.

Assymetric Canoes have slightly less than 250 ft in the spinnaker and slightly lower RM (I think, I don't have figures to hand) than the racked Contender....but the big kite is a bear to handle and as Doug points out, the (lighter) MPS and RS 700 have smaller kites and similar performance.

Tim, it's carbon with corecell foam and fairly light-16' hull+ tubes& seats about 125Lb.s but it is not the design I would now choose for a foiler. This boat was designed in 2000; for an improved version see the "Peoples Foiler" thread and the sketches by Eric Sponberg....

Tim, see my correction to post #4...

[TimClark]

Originally Posted by CT 249

When world-class Contender sailor Jo Rosler moved from Germany to the US and started sailing on LIS, he added a metre to the rig, a fully-battened main and a roller-furling reacher. He also experimented with wings....the width is on another computer but looking at my pics I think they were about 3' wide. However, he found that they tended to drag (they don't angle up much) and made the cockpit too much of an obstacle course.

I have seen this done on Contenders modified for 2 crew, but just as a fun boat. Can't really see why you'd need a bigger mast if you are just adding an assy; Canoes for example switch to an assy by just adding another set of stays and spreaders to the topmast.

Assymetric Canoes have slightly less than 250 ft in the spinnaker and slightly lower RM (I think, I don't have figures to hand) than the racked Contender....but the big kite is a bear to handle and as Doug points out, the (lighter) MPS and RS 700 have smaller kites and similar performance.

Do you know where on LIS he moved to? I am really interested in Contenders and want to meet up with a person that knows about them/take a test sail. Thanks.

Tim

[gggGuest]

Don't forget though that the asymettric/righting moment combination primarily controls how low you go on the run. With a smaller sail you point higher with more apparent but less vmg, with a larger sail you go lower with less apparent and better vmg. There's definitely a point at which a bigger sail is slower through the water, but the vmg improves. The other lmiting factor is the point at which the sail is so large that the normal shifts and gusts at your sailing venue are stopping you from controlling the boat. So on the whole for fun sailing my opinion is that a moderate sized sail will tend to be a better choice because you spend more time going faster. Arguably the IC is the exception because its so great going upwind that you want the biggest sail possible to get downwind over with so you can go upwind agsin [grin]

[frosh]

Interesting that the size of the IC kite has been mentioned on this thread several times. The current thread on the IC forum (UK) has a discussion going re kite size and visibility. http://www.intcanoe.org/forum/topic.asp?TOPIC_ID=393
What also is apparent that there is some frustration amongst AC owners that they are not able to hold kites on many offwind legs as I presume that the direction is not deep enough. The suggestion is made that if cost was no issue 2 kites should be owned and the one used depending on the exact course being sailed that day.
The other inference from that thread is that there are some safety issues with a really maxi kite which 250 sq ft. is for a singlehander.