Radial Jib Fittings: Hoyt and JPT

[lorsail]

Radial jib fittings can offer a two or three degree boost in pointing ability and are superior upwind for that reason to "normal" jib boom setups.
In the past radial fittings have been cumbersome and heavy.Then Garry Hoyt invented the Hoyt jib boom. The front end of the jib boom which can be made out of 5/32" stainless and the rest carbon is bent to go thru the deck at angle. This angle depends on how far aft of the forestay the Hoyt boom is mounted:take a line from the center of the Hoyt mounting hole to the intersection of the jib stay with the mast and glue in the Hoyt mounting tube at that angle. A Hoyt system can be added without reinforcing the deck by adding the mounting tube to a piece of glass or carbon about 1" square then add that unit to the deck. Doing it this way allows for later angle adjustment or adjustment of the distance between the mounting hole and the forestay. It is important to note that by having a small distance (.5"-1") between the forestay and mounting hole as the boom is eased the outhaul is automatically eased on the jib boom creating more camber in the sail.
An experimental system still being evaluated is the jib pivot traveler or JPT-it may be the best"radial" system yet. This is a very simple unit in princible: it allows the pivot point of a "normal" jib boom to slide across the deck so that when going upwind the forestay/boom intersection is directly above the boats' centerline.The difficulty lies in getting the pivot point to slide smoothly under backstay tension. This unit has been found to work very well in its first incarnation in light to medium wind; in stronger winds the teflon bearing sliding on a carbon shaft(track) did not slide well. New versions are being tried using a continuous loop of line stretched real tight and running between the sides of the front deck with the jib pivot attached to the top line in this loop. A version using a small rod and a pekabe bearing is also being tried. The JPT ,once the initial problems are worked out offers the best radial "action" I have ever seen and has the potential of being the lighest and most adjustable of "radial" fittings.The JPT also has a side effect downwind in helping keep the jib clear of the mains blanket and with an improved reaching set up over a normal jib boom. Its major disadvantage,so far, is lack of an automatic jib outhaul but its other benefits out weigh that I think. More info as it comes in....
Note: I'd post pictures but I can't with webtv so you can go to microsail .com and see shots of America One or the Spinnaker 50 both of which use the Hoyt Jib boom-no close ups though; no close up pictures exist of the JPT but maybe Dick Lemke will fly down and take some. Some of the guys experimenting with the JPT may post a picture and I may post a couple(with anonymous help?) -in a month or so if we use the JPT on the new F48 tri's....I'll send anyone that asks a rough sketch of either one; just e-mail me. lorsail@webtv.net
Doug Lord
microsail.com
monofoiler.com
High Technology Sailing/Racing

[wgorgen]

Dick,

The best piture I have seen of this system is on the F3: http://www.microsail.com/pictures/mfoilerf3_13.jpg

You can see that the jib is tacked to the deck and the clew of the sail is attached to a small boom that pivots in a hole in the deck about an inch or two behind the tack.

I've been looking at the Hoyt system as a possible replacement for the standard jib boom on my boat. It offers several advantages.

1) the camber of the sail will increase on the reach and run. The amount of camber increase is determined by the amount of offset between the forestay and the pivot. Personally, it looks like Doug might have a bit too much offset in his F3 design. This picture shows the jib shape on a reach and the jib is luffing quite badly: http://www.microsail.com/pictures/mfoilerf3_23.jpg . I think you want to get to about 30% camber on the run (from about 10% camber on the beat). So for a 10 inch foot length, you want the offest between the jib tack and the hoyt pivot to be around 1.35"

2) The jib clew is supported by the jib boom, so there is no need for a jib boom topping lift. This advantage can be further extended by having the hoyt boom rotate around a slightly different axis than the jib stay. That way, the jib leach will actually tighten for the run and you will not spill so much air when you are running wing and wing.

The trick is to get the system to work with the same low friction as a standard jib boom. If you can do that, you can practically sweep the deck with the jib which will reduce the induced drag of the sails and should help boatspeed.

Like I said, I am still playing with this concept. I have not actually built one yet. Maybe this winter in between all my canting mast project work....

- Will



Will Gorgen

[Roy Langbord]

Someone once said "There is many a slip between the cup and the lip"; in the case of r/c sailboats there are just as many slips between theory and practice.

Radial jib fittings have been around for years. Many have tried to make them work, most have been unsuccessful. They have about an equal number of advantages and disadvantages. They have more friction than conventional swivels, usually can't be moved to accodomodate different rigs, are complicated to build right and if out of alignment can cause a boat to track very poorly. If you look around at all of the classes sailing today you will see very few boats using radials and even fewer winning boats with a radial jib fitting (with the possible exception of the very expensive, very high tech and beautifully made Walicki Skapel radial fitting).

As to the "JPT". From others who have played with similar concepts, it would seem likely that the friction problem can not be overcome. And, if the moving jib pivot doesn't end up in the right place, you will have a very ill performing boat.

But the real answer to all of these questions is to actually built some of these concepts and try them out on the race course. Both of these ideas are legal in numerous racing classes; both have been talked about on the internet for almost a year now; both could have easily been incorporated on some boats somewhere during the 2003 sailing season. To date, however, no performance results whatsoever. Isn't there someone somewhere who buys into these ideas enough to try them out and report back results?

[lorsail]

The Hoyt jib boom is a requirement on a spinnaker boat and works extremely well on the ones I am familiar with-andhas for over 8 years.
The JPT is under development and is being experimented with by several people across the US-it has great pontential on non spinnaker equipped boats and may be standard on the new F100CBTF .
Anybody is welcome to try the Hoyt Jib boom or JPT....

Doug Lord
--High Technology Sailing/Racing

[BobT31]

the answer is ball bearings-
then again thats the answer to everything
"Its all ball bearings...."

[wgorgen]

Ok Fletch!

Will Gorgen

[Gio]

I do have a question: can you use a ?regular? jib with the Hoyt boom (or any other radial boom) or do you need to modify the sail somehow.
If I remember correctly when Steve Andre posted some picture of his ?radial jib assembly? he mentioned that he had to modify the jib in order to make it work.


Gio

[wgorgen]

Here is something interesting I came across the other day.

Peter Allen rigged up a loose fitted jib on his Soling 50. He raced it at race week in 2000 (which was also the national championship regatta that year) and won the regatta.

Here's some pics:
http://www.amya.org/rw2kpics/rw2ksodsn175detail00.jpg

http://www.amya.org/rw2kpics/rw2ksodsn175.jpg

Aparently it worked well enough to help him win the nationals that year.

Also apparently no one else felt it was worth doing because I have not seen it since then on any other Soling 50s or any other classes.

I would imagine that downwind he would have some trouble getting the sail to wing and wing well. It seems like you would loose a lot of downwind drive without that.

Does anyone else know anything about this? Has anyone seen anything else like this?

Could a "lazy" Hoyt type boom (one that did not really provide much lift or down force but only served to keep the clew pushed away from the tack) be used to help the sail wing out downwind? It seems like the boom would "sky" without some limiter on the amount of upward motion, but perhaps it could be loose within some up and down range....

- Will


Will Gorgen

[lorsail]

On Steve Andre's set up not only did the jib have to be modified but an extra line went from the front end of the boom to the mast.According to Marchaj a round line has the drag of a streamlined body twenty times larger. Steve says it works so it works I guess.
Most traditional radial jib fittings don't require any modification of the jib at all. That is true with both the Hoyt system and the JPT.
The JPT offers the additional advantage that the same boom can be used with the same jib.
The traditional radial fitting and newer Hoyt and JPT don't require any extra lines running up to the mast ahead of the forestay.

Doug Lord
--High Technology Sailing/Racing

[Gio]

Well, thank you Doug, that?s what I was hoping for.
I?m trying to see if I can include a ball bearing radial jib boom in my new boat using my old set of sails.

Gio