View Full Version : St Pierre motor wells
12-10-2004, 02:23 PM
new to group, I built a 27' St Pierre with 2 motor wells viewed at:
to accomodate 2 motors, i moved the wells forward one station (2.5'), which with the rocker raises the water level inside the well, resulting in good splashes of water getting inside the boat, especially with lack of ballast in the bow, which causes the boat to whack the water when coming off a wave.
I'm adding ballast in the bow, 4 sandbags on each side of the stem for starters. I have installed rubber boots at bottom of well and top of well to see what effect they have. I also have built an enclosure for the well and motor, which also serve as seats. will post results after trials this weekend. any suggestions will be welcomed. When I get the cash, I want seal up the wells and install a small diesel.
Neat, glad you shared the pictures with all of us. The boat looks like a lot of fun.
As to your problem, in my opinion, sorry but I think you screwed up.The boat has too much rocker to be moving motor wells around as you found out.
If it was me, I would bite the bullet and plug the motor wells back to original, then put in a single well as shown on the plans in the proper position. You have two 4 stroke 15 horse
outboards, I would think one would be plenty, or just right for that boat, after all it only has a top speed of 10 m.p.h. You may want to get a lower pitch prop though, to have more power at lower speeds. I wouldn't consider putting a diesel in it, after all, the glory of the boat is the single well with a low horse engine, so why waste the money and effort. The best part is now you have a xtra engine, so build another pierre and sell one. There is a st. pierre version made by nexus marine, where they have up to a 50 horse for some speed, but if you examine it, they took all the rocker out of the bottom, and it is now a different animal.
P.S. on the back of the motor well, it needs to be at a angle, not straight up and down.
[ 12-10-2004, 03:52 PM: Message edited by: RonW ]
12-10-2004, 04:00 PM
Hey Mark, welcome aboard.
I'm not real familiar with dory's but I do have some experience with outboards in wells.
Your wells look to me to be way to close to the waterline, perhaps dangerously close. The wells look like they would ship water with very little cargo weight. Usually outboard motors perform best if they are mounted with the cavitation plate +- 1/2" with the bottom of the boat, yours are extreemly deep in the water.
12-10-2004, 09:30 PM
Hello Mark, neat boat!
It sounds like you already know that your motorwell arrangement isn't workable. My only suggestion would be to NOT ballast the bow in an attempt to raise the motorwells. I think that would be inviting disaster.
Better, I think, to seal off one of the wells and run with one motor. That will give you more flotation, and reduce weight aft. As you have a rudder, I don't think an offcenter propeller would be a problem.
12-11-2004, 02:17 AM
Great looking dory.
Ballasting the dory bow down will likely cause the boat to wander making it more work to steer. Dories do fine with heavy loads as long as they are properly trimmed.
Do you have enough shaft length to raise your motor well height and still keep the cavitation plate near the boats bottom?
Also a rubber boot, or plug, at the bottom of the motor well even with the boats bottom will reduce drag significantly and keep the splash down. I've used a heavy tire inner tube with success. Cut a hole in it so it fits snug around the ob. The inner tube rubber is soft and stretchy enough so you can pull it over the prop and cavitation plate.
I also agree that one well and 15hp ob will be plenty.
12-11-2004, 07:25 AM
thanks to all for your comments. I'll try this:
- double boots top and bottom of well
- no ballast
- my cavitation plates are almost 2" down in the water, so I could raise the well height a bit till they are flush with the bottom, right?
12-11-2004, 12:29 PM
Righto Mark - cavitation plate flush with the bottom will be good. The exact location is not critical in a displacement boat.
Hang ten dude (that's my weak attempt at sounding like a surfer).
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