Bertram31.com General Bulletin Board

For those long on grey matter

Posted By: brianb
Date: Saturday, 22 January 2005, at 6:13 p.m.

I ran accross something interesting that I cant quite figure out.

A repowered boat(not a 31 but very similiar). The struts, shafts, engines were changed out. After the process, the charicteristics of the boat in reverse were radically changed for the worse. It plows a lot more water, and has to be driven very carefully, because it seems the transom could be driven underwater at 7+knts.

The shaft angle stayed the same, but the strut location and shaft length changed. I believe(after measuring) that the strut(rear face nearest the prop) was farther forward by a couple of inches, and the shaft was shorter by the same amount.

Could this movement of the strut/shaft/prop further forward cause the change in handling in reverse? I had never considered the balance associated with the location of running gear to be so important in the overall functioning of a boat.

I know under my engine hatches, I could move an engine up or down probably 4" overall, and with the same set of stuts, and same shaft angle, this would cause a big shift in the location of a strut on the hull. This would also change the distance between the strut/prop and the rudder, with would also effect the handling via rudders.

I bring this up, because in discussions on this problem, with someone that has what i would consider good experience, he felt all the dimension in the changes were ok.

What changes in dimension would be considered ok, and not truely effect the boat? Could the change in strut location to further forward cause this problem? I also wonder if this change would effect the top end speed due to more downforce on the bow of the boat, through lessened overall length from the prop to the bow?

Over time I have also noticed on the board a range of shaft lengths on 31's. I would think that the shaft length and strut distance below the hull should be fairly similiar on all 31's. I have noticed as much as 8" difference in shaft lengths over the past couple of years in posts. Does this mean that these 31's should handle differently?

Your thoughts, I would like to be educated on this topic?

Brian

Messages In This Thread

For those long on grey matter
brianb -- Saturday, 22 January 2005, at 6:13 p.m.

Re: For those long on grey matter
Capt. Dave Kosh -- Monday, 24 January 2005, at 10:43 a.m.

Re: For those long on grey matter
brianb -- Monday, 24 January 2005, at 10:13 p.m.

Re: For those long on grey matter
andre fourrier-Louisiana -- Monday, 24 January 2005, at 10:30 p.m.