39ft wooden motorsailer

[Steve W]

Hi all,i have an interesting project in the shop.A customer bought a rather attractive project motorsailer from a storage facility in Milwaukee and had it shipped to us to complete.We dont have much info other than it was built in Finland in 1970,made its way to California for a while,was bought by a guy in Milwaukee who used it for about 7 yrs before hauling it at this storage yard and tearing the entire cabin structure off down to the deck and then strip planking new sides on,thats as far as it got.it then sat (indoors) for a decade,enter our customer.Now a little about the boat itself.Its 39ftx34ft8"x12ftx5ft2".It is canoe sterned and the hull in profile looks very much like a Banjer 37.The entire boat is in quite remarkable condition,the topsides are bright finished (yellow pine) and in great shape,no decay or even discoloration around the fasteners,it has high bulwarks and a loverly sheerline,there is no rot anywhere so it was certainly worth saving.Unfortunatly we have no drawings or even photos of it prior to the cabin being removed so i drew the profile and then designed it as an aft cabin pilothouse,that part is now finished.Now it gets interesting,the boat came to us with wooden spars,again,no rot but the glue had failed on the main mast which i dismantled reglued and painted before gradually realizing that it dosnt belong to this boat,also the boat had originally had internal ballast which was long gone except for about 1200 lbs of lead ingots way up foreward.At this point we realized that i was going to have to do a complete redesign so i have taken off the lines,calculated the displacement,Lcb,weighed the actual boat,the spars etc,mesured the tankage and estimated all the weights and figured the Lcg,drawn the sail plan and compared what i have with the stats of all the similar boats i have found online and so far everything looks good,i am now getting ready to cast the ballast which will now go on the bottom.
About the only thing i have yet to figure out is how big a rudder i need as a percentage of the lateral plane,the existing rudder is only about 5 sq ft,i think i probably need about 3 times that which will be hard to achieve.I have about 167 sq ft of lateral plane with the new keel.Any help would be appreciated.
Steve.

[lazeyjack]

15 i think is far to big a plan, by far, nine would be more than enough, canyou sketch what you have down there

[Steve W]

Hi Lazeyjack, i have found very little in any of my reference books on rudder size although Dave Gerr uses .068 x dwl x draft and Brewer uses 8% to10% of the total lateral plane,interestingly both these methods give 13.36 sq ft for this boat.I am not savy enough with a computer to post sketches or photos,sorry but if you google banjer 37 the side profile is very similar.
Steve.

[lazeyjack]

the rudder here looks to be abt 2 ft six by 3 six max, it is allready low aspect, I would not go with wider chord, but would try get it as close to the bottom of boat as possible, About the only positive about the rudder here, is that its positioned well aft , 15 sq feet would be over double the size, or 1.5 sq /m
I would narrow the chord abt 4 inches and take the top in line and close to the hull

[Steve W]

Thanks Lazeyjack,the existing rudder is about 2ft chord x 2ft 6" high and is very thick,about 4". I can probably up that to 2ft 6" x 4ft,about 10 sq ft, i need to angle the bottom up some so it is not the lowest point,the entire hull profile is very much like that but i am adding a ballast keel that is 20" deep fwd tapering to 12" aft which brings the bottom closer to parallel to the waterline and increases the keel span,draft has increased by 6" to 5ft 8" which is still reasonable.
Steve.

[lazeyjack]

Thanks Lazeyjack,the existing rudder is about 2ft chord x 2ft 6" high and is very thick,about 4". I can probably up that to 2ft 6" x 4ft,about 10 sq ft, i need to angle the bottom up some so it is not the lowest point,the entire hull profile is very much like that but i am adding a ballast keel that is 20" deep fwd tapering to 12" aft which brings the bottom closer to parallel to the waterline and increases the keel span,draft has increased by 6" to 5ft 8" which is still reasonable.
Steve.

sounds good , nice idea to balence 17% here is a good link, if you sketch the plan and scan it, and give me the stock thickness and detail botton brg I will gladly draw it in rhino for free
http://www.boat-links.com/foilfaq.html