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Bigger Sail for a Sunfish

taobsu1

New Member
I usually sails in a small reservoir near by. The typical wind condition is very light
less than 10 mile/hour, around 5 mile/hour most of time. I am thinking of speed up
boat with more sail area, by streching spar length in order to fit a bigger sail.

The current length of spar is about 14 ft. By increasing mere 3 feet each spar, I can add about half (44%) of sail area from class sail. I know the modified boat is gonna to be tippy. But with stable sunfish hull, and my heavy body weight ~200lbs. It might not that too bad compare to laser, or even mention a skiff, such as 29er.

Has anybody tried that before? Any suggestion?
 

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matias

Member
I usually sails in a small reservoir near by. The typical wind condition is very light
less than 10 mile/hour, around 5 mile/hour most of time. I am thinking of speed up
boat with more sail area, by streching spar length in order to fit a bigger sail.

The current length of spar is about 14 ft. By increasing mere 3 feet each spar, I can add about half (44%) of sail area from class sail. I know the modified boat is gonna to be tippy. But with stable sunfish hull, and my heavy body weight ~200lbs. It might not that too bad compare to laser, or even mention a skiff, such as 29er.

Has anybody tried that before? Any suggestion?
how are you going to make the larger sail?
are you gonna make it yourself?
 

taobsu1

New Member
how are you going to make the larger sail?
are you gonna make it yourself?
Yes, I was thinking to add one wide strip attach the real end of original sail.

My concern is if I need compensate with possible slight shift of center of sail area (which wind force acts on) with other change, such as rudder and centerboard shape.

I heard the term of 'Weather helm' , is this will likely occur? How big of effect for such change?
 

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matias

Member
Yes, I was thinking to add one wide strip attach the real end of original sail.

My concern is if I need compensate with possible slight shift of center of sail area (which wind force acts on) with other change, such as rudder and centerboard shape.

I heard the term of 'Weather helm' , is this will likely occur? How big of effect for such change?
if you are getting larger spars you´ll need a larger mast and larger blades too to compensate the amount of power you are getting from the sail
 

surfski

New Member
You are suggesting 44% increase in sail area ?????? By the time you make accomadations of design you may just as well try a bigger boat. I would venture that the radical change to sail area you are suggesting will not only create a bunch of other problems , It won't improve performance in the light winds you have mentioned. IMHO of course.
 

Wavedancer

Upside down?
Staff member
Boats are designed to have some weather helm. This is a safety issue and means that if you let go of the sheet, the boat will turn towards the wind and stop. This in turn, will allow you to get back after you get separated from the boat.

As Matias already pointed out, you are thinking about changing the rig pretty dramatically. In very light winds, the boat might still sail OK, but in moderate breeze, the blades will be undersized. Also consider that you are changing your rig irreversibly. Are you going to insert some sort of pipe to extend the spars?
 

taobsu1

New Member
if you are getting larger spars you´ll need a larger mast and larger blades too to compensate the amount of power you are getting from the sail
I try to make minimal changes as few as possible.

The original mast seems ok if still use point A and B as previous way of rigging. One question though, that is if the shift of Center of Sail Area (from point C to D, see picture) is too much while dealing with light wind. Rudder blade looks too small need to be increased in order to counter the torque created by the Center shift.

As said by Wavedancer, I plan to remove caps on the end of spar, stick 3 ft tube into it.
Again, my plan is try to use in light wind condition. Hope it can plane in 5~8 mile/hour wind.
 

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beldar boathead

Well-Known Member
There is one way to find out if this will work = try it! However, sailboats generate power by flow over the sail. Unless you know what you are doing, that "extension" on the sail is going to have serious flow problems as the air moves from the original sail onto the extension. It might end up just being drag and you could end up with less power.

On the "general" part of this site, there is a guy selling a "bigfish" which is just a really huge Sunfish. He says the boat has 114 sq feet of sail. Maybe you can find just a bigfish sail for sail, and then put it on extended spars. That way at least you will have a quality sail.

Good luck! BB
 

taobsu1

New Member
You are suggesting 44% increase in sail area ?????? By the time you make accomadations of design you may just as well try a bigger boat. I would venture that the radical change to sail area you are suggesting will not only create a bunch of other problems , It won't improve performance in the light winds you have mentioned. IMHO of course.

Yes.

I got my used Sunfish for $400. If I just experiment by making some temperary changes what I can lose. I doing windsurfing before. It is typical to choose your sail depends on the wind condition for windsurfer (for examples, 4sq meter, 5 sq-meter, 6 sq-meter). It seems to me dinghy sailor can adapt the same approach.

Plus, my guess is the Sunfish design will be intended/optimal only for stronger wind condition, say 12 mile/hour to 20 mile/hour. It is pain on the neck when your boat can not go on plane.
 

Wayne

Member Emeritus
Maybe you can find just a bigfish sail for sail, and then put it on extended spars. That way at least you will have a quality sail.
You can go to Island Packet Yachts and get a Big Fish sail and spars right over the counter.

You could also get a Minifish and fit it with the Sunfish rig. That's probably the easiest way to accomplish the turbo-charging effect with a boat and sail you know will work together.



_________________________________________________

There needs to be balance






Center Of Effort by Dave Acree
http://www.myrc.org/Library/centeref.htm

Balance Your Helm for Speed
http://johnellsworth.com/writing/nautical/balance_helm/balance.html

The physics of sailing
http://www.animations.physics.unsw.edu.au/jw/sailing.html

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taobsu1

New Member
_________________________________________________

There needs to be balance






Center Of Effort by Dave Acree
http://www.myrc.org/Library/centeref.htm

Balance Your Helm for Speed
http://johnellsworth.com/writing/nautical/balance_helm/balance.html

The physics of sailing
http://www.animations.physics.unsw.edu.au/jw/sailing.html

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Wow! That is a lot to chew on.

Thanks for the reference.

I will take time to do some precise calculations see where my new CE(Center of Effect), and CLE ( Center of Lateral Resistance). If the shift of CE causes problem to maintain basic weather helm, I might have to increase the height of mast ( so I can shift the whole sail forward with higher hanging point for the up-spar).

Personally, I believe the length of spar of current 14 ft, is bound by the length of boat for the shipping purpose. Other than loss of some of sail efficiency while increasing the sail area, there are no foreseeable factors against boat speed increasing. Granted, any such change might bring trouble in control the boat. I think the Sunfish hull has more stability reserve (than Laser). So the worst I can get is a Turbo-Sunfish tippy as a Laser. It is not bad compare to a skiff in terms of how often you have to swim.

BigFish is a very cool boat. From what I've seen, it is a blow-up (propotional) Sunfish to the LOA 17 ft. The purpose is for carry more people. Its ratio of Sail Area / Displacement might not change too much compare to a Sunfish. So I think the performance will remain close to Sunfish. I will call their Maryland dealer later to see if the mast fit Sunfish's.

The price of BigFish is about $5000. I think their parts will not cheap. I might have to roll up sleeve DIY.
 

Wayne

Member Emeritus
Wow! That is a lot to chew on.
I'm not saying chew on all that physics. Just showing that if you want to make a design change that truly effects performance there are some concepts of balance you need to be aware exist.



I might have to increase the height of mast ( so I can shift the whole sail forward with higher hanging point for the up-spar).
This can also be accomplished by making the boom adjustable in the gooseneck by installing a quick release pinch bolt.



Personally, I believe the length of spar of current 14 ft, is bound by the length of boat for the shipping purpose. Other than loss of some of sail efficiency while increasing the sail area, there are no foreseeable factors against boat speed increasing.
Keep in mind the Sunfish was designed as an all around sports boat, easy to learn sailing on. Performance enhancement typically comes after first time owners master the basics.



The price of BigFish is about $5000. I think their parts will not cheap.
If you hear of any full range of boat parts that come cheap, please let us know. :D

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