mainsheet / boom
 

I'm new to rc sailboats. is there any reason the mainsheet is led to the middle of the boom instead of the aft end of it ?
thanks
dr

RE: mainsheet / boom
 

It it usually determing by the limit of travel (or "Throw") of the radius arm of the servo. For Simplicity, If you have a full 180 degree servo, the max line that can be hauled in is 2X the length of the servo arm. For a 150 degree servo it's going to be less than that. If you take a pen and mark the line on the main where it exit the boat at closed hauled and then again with the sails full out, you will find that is the same as the "throw" of the servo arm. To attach the line farther out on the boom would require you to haul in more line and would require: A. Lengthening the servo arm or B: modifying your servo for 180 degrees (mentioned elsewhere), or C: both A & B. At some point however, you will find that the servo arm would no longer fit into your boat. Conversely, moving the attachment point closer to the boom would require less throw but require more torque on the servo. (larger servo, heavier weight, more cost). Anyway, that's the basic design limitations that determine where the attachment point is on the boom [sm=confused.gif]

RE: mainsheet / boom
 

Presumably the main and jib have to move more or less in unison and tha much shorter moment arm of the jib to its pivot point limits the length on the main.

RE: mainsheet / boom
 

Guiri,
Ah, but the attachment point of the jib control line isn't necessarily the same as the main's control line. If the jib's line is attached closer to the servo than the main's line, the amount of jib movement can be varied quite a bit.
- 'Doc

RE: mainsheet / boom
 

Ah Ha! that makes sense. now I have to find something to use for turnbuckles and vang.
thanks.

RE: mainsheet / boom
 

Til you find the exotic hardware, there's an awful lot you can do with some stiff nylon chord and bowsers/bowsies and/or cleats... in fact, that's how the vang was rigged on my full-size boat.

RE: mainsheet / boom
 

dr2;
On one of my 50-800 boats I have a 3rd small servo that the Jib sheet is attached to via a pulley on the end of a 3" servo arm which gives me Jib trim of approx. 6".
The sail winch still controls both sails in unison, but having Jib trim does make the boat go a bit faster. It does take a 3 or 4 channel radio.

RE: mainsheet / boom
 

I'd have to interpret that the real intention here to be that the skipper's skilfully trimming the jib MAKES the boat go faster while having jib trim ALLOWS THE SKIPPER to do that skillful trimming... so my question:

As the skipper, how do you trim the jib properly? My guess would be to allow it to default to a neutral setting and then adjust from there, judging the goodness of the trim from sail set and speed change? (This is essentially what I do when I'm physically ON a boat.) Can one effectively observe those things from the shore? Or are there other indicators or even other techniques used?

RE: mainsheet / boom
 

Wow. thats complex. When I race, I just do it so that boat is healing and the telltales are straight. and I let my crew do his job;)

RE: mainsheet / boom
 

You mentioned making a 180 degree servo. Where is the link? I have a Futaba sailing servo (not a winch) I would like to convert to 180 Degrees.

RE: mainsheet / boom
 

dr2
could you tell us size/type of boat you have ? depending on how big, there is a bunch of DuBro items in either 2-56 or 4-40
that can be used for rigging, ie: plastic or metal clevis's are very commonly used on the end of side stays , hooked into a screw
eye or screw bolt . a vang can be as simple as a line with a bowsie , or a rigid vang can be cobbled from DuBro parts also.

where in Illinois are you ? if your near Chicago come visit our club some Sunday -I can pm you contact info.

oh, I just went through what you are doing, got an old boat from a club member, funny the booms wouldn't go out far enough.
checked against the plans, oops - the exit holes on the deck were in the wrong places. then made sure the attachment points on
both booms were right above those points and hey, booms go all the way out now.magic..
Allan

RE: mainsheet / boom
 

http://www.servocity.com/html/180o_servo_stretcher.html

$20. 180 degrees instead of 90. Works great. First make sure that your servo is capable of turning 180 degrees. Some servos have a stop that limits the turning to less than 180. I do not think you will hurt the servo by turning it by hand.

You can take the servo apart and file down the stop, but you might not feel comfortable doing that. That is shown in the US1M Construction Guide which is online. !80 degree conversion is also shown in the guide on page 51.

http://www.theamya.org/boats/us1m/us1mcons.php

Page 53 near the bottom of column 1 talks about filing the stop on a Futaba servo. I believe some Futaba servos are willing to already turn 180 when hooked uo to a servo stretcher and some have a stop that limits them to slightly more than 90 so need to have the stop filed off before hooking up to a servo stretcher.

RE: mainsheet / boom
 

To allow for the main sail to go further out when sailing downwind.