Leeboard Location Question

I’ve been through all the houseboat posts and haven’t seen anything to answer the questions I have.

I will be retiring to the Bocas del Toro area of Panama soon having recently received my Pensionado visa. I plan on building a houseboat there and have several ideas. I like George Buehler’s “Rufus”

 

Old Salt,

Welcome aboard! The placement of the leeboard can't be known until you decide what the rig is (and where its center of effort is) along with whatever lateral resistance the hull will have. This is because the lee board is really just an additional piece of lateral resistance that is added onto the rest of the hull's shape and the rudder. So, once you've decided where the rig goes, how big it is and calculated the center of effort from the rig, got the hull designed, then at the last minute you can attach the lee board.

One of the GREAT things about a lee board is that if you design it right you can move it up and down. This will not only get it out of the way of rocks, trees, etc... it will allow you to move the center of lateral resistance fore and aft. As the lee board is lifted it will move aft and that will tend to reduce your weather helm. Move it forward (down) and it will tend to give you more weather helm. As a result, you'll want to design the lee board so it can be used while sailing at every position. I'd suggest that you'll also want to do a design that allows you to experiment with the position. Meaning that you clamp the lee board to the rail in one place and then go sailing to test your design. I'm pretty sure that unless you're a naval architect (and even if you are) your first guess on the position of the board will be wrong. Move it around until you're happy and then attach it for ever.

On the Gaff Rig vs the Marconi or Lugger, I wouldn't be too worried about the rigging. You don't have to do a gaff with multiple falls on the peak halyard, modern lines and winches make it a snap to have a gaff with only two halyards, that's only one more than a marconi rig. The main reason you might want a gaff is because it has a much lower mast height required for a given amount of sail area and there may be bridges you'd like to get under. Finally, if you're looking to have a salty looking boat, add a bowsprit. It's easy to remove a bowsprit that is designed for it and stow the spar along the deck (it's what the traditional hay barges did in San Francisco Bay) when you're tied up to a dock or pier. Bowsprits have all sorts of great features, like being a place to hang the anchor from, hang a jib from, balance the rig with in case you've got too much weather helm.

The reason I keep bringing up weather help is that most designs end up with way too much of it.

Finally, if you're primarily going to motor this boat, I'd suggest putting the motor in the middle and having two rudders on either side. The reason for two rudders is to let you make them very shallow and still big enough to steer. It let's you get the motor in the middle, so you won't have it trying to turn the boat all the time you're underway, and it's easy to rig together by attaching the tillers with a tie bar.

Have fun! Sounds like a great project. I'm now thinking about a Delta Barge much like this. It's a great idea!!

Beau

 

Look at the picture you posted. See the dot in the middle-ish of the sail? That is the Center of Effort of the sail. The CE of the sail is balanced with the Center of Longitudinal Resistance or CLR of the hull and the appendages...including the Leeboard. The CE of the sail needs to lead the CLR by a percentage of the Length Water Line or LWL. In your pretty square shaped hull it would only need to be a couple of percentage points...say 2 or 3 percent. On a 30 ft hull this would only be between 7 and 10". Your leeboard needs to be parallel to the centerline of the boat but with straight sides you don't have the problem of finding maximum beam. Balance adjustments are made by pivoting the board aft to shift the CLR aft. For Beam reaches, Broad reaches and runs you shouldn't have any difficulties if you go with setting the middle of the CB (when vertical) directly under the CE of the sail and having a bit of a skeg and the rudder area set your CLR a bit aft of that. This also assumes that the CE of the sail lands somewhere near the middle of the LWL. If it is significantly forward or aft then you would need to re-calculate things a bit more.


Just my opinion of course and there are others here who are more knowledgeable and experienced than I.
Steve

 

Finding a Sail's Center of Effort

How do you determine where a sail's center of effort is?

 

http://www.jimsboats.com/1aug08.htm

This will give you the directions to do the math (and Geometry) for finding the CE

 

The leeboard's placement is very limited by the hull form selected. Unlike other retracting appendages, leeboards really have only one place they can live and be effective.

Understanding the fundamentals of design work would be a prerequisite I'd suggest, for a reasonable expectation of success, particularly in an odd rig, appendage, hull configuration or arrangement.

Setting nearly 400 sq. ft. of area on a Bermudian cat rig (with or without a sprit boom) would be quite a tall mast and a bit of wasted luff length. You'd get more "bang for your buck" to go with a quadrilateral sail, gaff, sprit, lug, etc. The CE would be lower, reefing wouldn't move the CE as much and bridge clearance issues could be avoided. Then again you could set up a cat ketch with free standing, Bermudian and sprit booms. This would keep your CE low, make more manageable area easily reducible, offer steadying options and you could fly a mule in light air.

Considering the basic nature of your questions, you should strongly consider purchasing a set of plans that closely offer your hydro and aerodynamic needs, rather then cobbling something together.

 

I believe he said he wanted a loose footed Sprit rig so I assumed a Sprit sail with no boom...did I misread? If not then all I have suggested is valid. If you go with a LOM with a Sprit boom then things will change somewhat but you could go with a gunter style mast and you can still clear bridges by lowering the topmast and reefing. His houseboat style hull has lots of center parallel side area so the location of the leebloard is problematical.

Steve

 

I also propose the same the ideas as BeauVrolyk
nl have it loose at first to move back and forth and twin rudders

here is a bit more info from Wynands site - look around all sorts of interesting bits and pieces

http://www.steelboatbuilder.com/tech4.html

it could be a very nice boat if executed well
marine ply and epoxy is not that difficult

 

No, you got it right Steve, I miss read the post. I dislike the idea of any loose footed sail for off wind work. They just lack control, though can be powerful if you can dog them down enough to get some shape.

Again, if you have to ask about the simple geometry required to find the center of a 2D shape, then it's very probable you'll need professional assistance in placing your centers, developing a rig, appendages areas and location, etc.

For what it's worth, a "Rufus" type of hull, with whatever rig atop, would sail worse then a garbage scow. I also suspect it would be a hard mouth thing in all but very light air, as arranged. Currently Rufus is carrying what looks to be at least 15% in lead (probably should be considerably more). With the sheets well eased, she'll be a handful to say the least.

 

I appreciate all the input to my questions. Some go far beyond the call of duty.

When I finally get down to Panama I plan on building the Brandy Bar Houseboat. The question regarding lee boards and sails as auxiliary power where a whim based on the fact that I thought the Rufus idea was cool. Primarily the boat will be outboard-powered. Any sail or lee board additions would simply be a lark. Since there are no bridges anywhere around the Bocas del Toro Archipelago mast height is not a consideration. In fact, I was even thinking of possibly using a small tree trunk for the mast and a polytarp for the sail.

Would the hull sail worse than a garbage scow? Probably, but I really don't care. The idea was simply the possibility of reducing the amount of gas used from time to time poking around the area.

But thanks for all the replies.