WSU Senior Project: New boom vang bracket

[tripdog7]

I am a senior at Wayne State University in Detroit majoring in Mechanical Engineering Technology. For graduation, the final requirement is a Senior Project. (your major thesis) I've decided to design and engineer a new mast fitting for the S2 7.9. I have crewed on Habenero in Lake St. Clair and the owner Sam gave me the idea for this project, as the current vang bracket is not an ideal design. My goal is to design a compact bracket that can handle all the stresses seen on this boat, and also allow the mast to be lowered without removing.
Does anyone have any advice on what they'd like to see? Materials, pin dimension, size, fastener type, anything???? I am having difficulties calculating the maximum forces seen on the vang. Any suggestions to help me create the best project are appreciated. I have a friend who works in a tool shop, and I plan on having this part machined to give it a proper sea trial. If successful, many I'll have a few dozen pieces made. (nothing like a little entrepeneurship!)

Thanks,
Paul

[Tom Line]

Here are a couple of suggestions:

Go all stainless on the fasteners.
S2 used metric rivets in between english rivet sizes. You can go 1/4 but that requires a special rivet gun. Go a size smaller (3/16) and you can buy the gun at any home depot for $14. Stainless again.

Find out what type of end block sam is using for his mainsheet and look it up online - you can get the safe working load and breaking strength then use those to figure the strength of your bracket.

Quick connect pins are a plus, and remember no sharp edges!

BTW, there are already brackets out there that do this. I have one on my mast. Quickvang I believe.

http://www.pyacht.net/cgi-local/SoftCar ... MASTF.html

[tripdog7]

Thanks for the advice. However, the one item I still need is the forces exerted by the vang. I disagree with using the working load of the mainsheet block as a design criteria. The forces required to flatten the main going upwind in strong winds would be the maximum down-force required by a vang. A quick search of the vang system out there for this size boat show a typical 8:1 purchase. This would exert an 800 pound load with a crew member pulling with 100 pounds of force. Throw in a 10% safety factor, and we're looking at abolut 900 pounds of in-line force on the vang. Do my assumption seem correct? Any sailing engineers out there?

Thanks,
Paul

[Tom Elsen]

A quick search of the vang system out there for this size boat show a typical 8:1 purchase. This would exert an 800 pound load with a crew member pulling with 100 pounds of force. Throw in a 10% safety factor, and we're looking at abolut 900 pounds of in-line force on the vang. Do my assumption seem correct?
Thanks,
Paul

Hi Paul
This seems pretty close to me.

You can check your estimate by using the downforce exerted by the mainsheet and then doing the trigonometry to get the force applied at the point of connection for the vang. I'd guess that the maximum force applied by the mainsheet trimmer is 125 lbs., on a 4:1 system. Figure you lose 10% to system inefficiency and you get 450 lbs of load.
You'll have to do the trig, as I don't have the measurements for the vang connection points to the boom.
Good luck.
Please post your results.

[tripdog7]

I completed my senior project on a mast fitting for a 7.9 boom vang system. This included a 30 page research document and a 12 minute presentation to the faculty and senior class. It must have been okay, as I was graded an A- overall, with an A on the paper and B+ on the presentation. I'm still waiting for the actual part to be made by my CNC programmer friend, but thanks to Sam B. of Habenero for the design, and my research for the engineering, everything is there.

Okay, so if I continue on for a masters degree in business... here's a new graduate thesis idea that we discussed.... build a business case model for buying the S2 7.9 molds and start a production run of new boats. Figure what design improvements could be made while staying in class rules (strengthened bulkhead, added floatation in case of swamping, etc). Lease a building with overhead cranes near a large lake. Then you'd need some fiberglass experts to build up the hull, topsides, keel, and companionway. Contract various hardware suppliers for the rigging. Then get a seamstress maker to produce some nice cushions and interiors. Hang a lightweight outboard off the back. Get a dealer distribution network together, offer a cruising and racing equiped packages, and there you go! I wonder what the profit margins would be for such a project? How much capital investment would be required for start-up operations? Is there indeed a market for a modern 7.9? Hmmm, very interesting for me and my fellow engineering sailor friends. Any thoughts?

[Coldduck]

Water is not critical for the manufacture - as a trailerable boat you could build the boats anywhere. Most of the big companies are farming out the actual fiberglass work or even the full build. The real challenge is marketing and developing the nitch market and hitting the right price point.

A company recently did the same thing reviving the Hobie 33. The new boats are listed at ~$55K. I am not sure how sales are or how many new boats are being built.

http://www.spartanmarineco.com/

Sadly most of the current manufacturing wisdom is to build off shore where environmental costs, labor and overhead are lower. The best model may be a mix of domestic and off shore manufacturing.

I am not a fan of off shoring but it is hard not to look at it when burdened labor rates over seas are ~$5/hr.

Good Luck!

[Guest]

Hi Tripdog7--

Not trying to dash enthusiasm for putting the S27.9 back into production but before you make any other considerations, you would be well advised to see if you can purchase the molds and rights to build the boat from the Slikkers family. It is my understanding that the S2 7.9 molds are the only molds they kept from their sailboat days prior to becoming Tiara Yachts. If they are not willing to sell, you will not be able to put the boat back into production. If this is merely an academic exercise for a thesis then you need not consider this but if you have intentions of actually following up on your thesis (as did Roger MacGregor), you will need the the legal rights and they may not be for sale.

[randy]

Guess anything is possible, Schock is starting a production run on the Wavelegth 24 again. They are selling it for 36K but they already have a production facility and the molds. Good luck with the project, I'd be very interested in a new 7.9.