I think I will spend some time with thoughts on your setup, though I have not had experience with your specific boat. However as I owned and sailed many years from Marina Del Rey, tripped to Catalina, Channel islands to San Diego, Wooden Hull owners assn. racing my Mc Innes (wood) – Coaster 25 cutter, Windsong, a full keel wood cutter, before that a Cal 27 sail # 45 as a half ton racer which I put a four ft. wide crack just aft of the main fin. Broke it in 20 ft. swells off point Huenemi racing and darn near went down, cabin cushions floating at the dock.
Plus several more smaller trailer boats, still have four now in fact. I have a bit of thoughts on the Spray – and have a Bruce Roberts book on his boats in general. The Spray offshore 40 is among them, an older book probably. I am familiar with Choi Lee 32 's, sailed on the PC class "Pirate", Kettenberg 40 s' and more. Age slows you down, so not as comfy on water as I used to be, but still build and boat constantly when I'm not on my motorcycle.
You really might consider the drag under sail of two pods. Check the sailing on the Westerly (British) series of twin keelers, they lose too much windward ability - as twin keels or twin props would. As a first thought, you will lose windward ability, and overall speed under sail especially to windward, with motors heeled over. Clean tacking would be non existent, mostly. Potential for damage from debris, kelp hang up under the hull, and general reduced performance. Using copper in any paint on aluminum, is a recipe for disaster, salt water makes any two dis-similar metals into junk. There are special non metallic paints that work better. The prop should be centered behind the keel for the reason that the keel protects it, any submerged log or piling could tear those pods off and is basically unsafe.
An example, check your California marina Del Rey coastal chart, forgot the number but --- just south of MDR and Ballona creek, Manhattan beach ok ? look at the pipe line marked as outflow, that goes out over 400 yards – covered by 4 ft. at mean low tide, sometimes lower. A buddy sailed over that, and got a broken arm, pitched down the companion way, ouch !! But wait, the prop shaft was bent and stuck so he called the coast guard Manhattan beach as MDR was tied to another job. The newish crew ran over the same pipe like at 40 mph trying to get to his Kettenburg K-40, which is about six ft draft = or- ok !! The coasties lost both shafts ripped out of the hull and damn near sank on the spot. The navy got a call and flew / dropped more equipment to clean up the mess. Oh, yeah put a big dent in the lead keel, sprung keel bolts and opened seams, about two grand to fix in 1960 something.
I have run over stuff, boat parts, deck cargo, logs, and more over 20 years sailing there. Do yourself a favor, electric is great, there are ways to get the electric power you need and keep the prop protected as it needs to be. I won't go into that here, because it is equipment that is originally for other uses, but would work very well and safely for your larger weight sailing hull application, even with pods by the way. However, as that is a big boat, and can use the battery pack with the gen set you need anyhow, for long term power. There are, however rudder designs that might do what you want with way less hassle. Designs from aircraft wing symmetrical sections that could be adapted to fit - from articles I have read.
I don't think I would open myself up to do something that will not be of benefit to a safe application. I said I would not hurt another persons dreams, but in retrospect, this is not a safe way to go, more expensive to make work, and offers not enough advantage over the regular way. On a deep keel boat, two props are more pain than pleasure, and will not turn or reverse like a power boat. Hull speed is pretty finite too, so no speed advantage either.
Sorry if this bothers your ideas, but please think about renting, or borrowing twin small 12 volt Minn Kotas, and some friends say 20 / 27 ft sail boat with a swing keel, at a longish angle. A 2 by 8 in. board across the gunnels about where the pods would hang with the two motors on it as a "mock up". When in light wind, check your GPS, drop the motors down, and do the math, half knot drag == maybe over twice that on a big boat, then try to steer it with the keel 3/4 down. The full keel will be a lot more "pod" and prop drag under sail. The further forward the less steering force you have, so don't do this close to anything. A trial horse of what you want, and a good cheap way to test it out.
Please don't let me rain on your parade, if you do this, and it works well, I will be very happy for you, sincerely !! All the best, ---- Cal
Sent: Friday, September 26, 2014 5:56 PM
Subject: Re: Just a Note on electric lower units
Thanks Cal, Thease are picture of my boat that I am building. The type of hull is a 37ft Bruce Roberts Spray sailboat, fair amount of curve but this is a new construction so modification is easy at this point. it is planned to be in saltwater for extended periods of time. thinking of painting everything below the waterline with Epoxy Copper paint. I'm thinking that two of these pods would be enough (say 5Kw each) on either side of the Keel and just in front of the rudder. This would provide for excellent maneuverability which would come from a large rudder and two wheels that can be reveresed during dockin manuvers.
please send me pictures if you have them of the modifications your local shop did?
Sal
Paso Robles, CA
