Planing on the Chine

[DCockey]

The boat referenced in the first post has an outboard well. Both Codega, and Blount and Schliecher emphasise ventilation of the bottom, particularly aft, as a potential cause of roll instability. I wonder what the effect of the outboard well is compared to a similar boat but with a bottom which is solid to the transom. Photos of the boat are at http://www.flickr.com/photos/37973275@N03/

[tom28571]

Originally Posted by DCockey

The boat referenced in the first post has an outboard well. Both Codega, and Blount and Schliecher emphasise ventilation of the bottom, particularly aft, as a potential cause of roll instability. I wonder what the effect of the outboard well is compared to a similar boat but with a bottom which is solid to the transom. Photos of the boat are at http://www.flickr.com/photos/37973275@N03/

Probably nothing. If anything, I'd expect there might be less ventilation in a well boat because of the hull extending beyond the transom much like sponsons. I believe the aft rocker on most Carolina Sport Fishermen is there to hold the bow high and keep the highly warped forefoot clear of the water as well as lessening the very sharp bow plunging deeply into waves. Holding the highly warped bottom bow sections clear of the water would lessen the tendency to develop the suction Blount attributes the "non oscillatory instability" to.

[DCockey]

Originally Posted by tom28571

Probably nothing. If anything, I'd expect there might be less ventilation in a well boat because of the hull extending beyond the transom much like sponsons. I believe the aft rocker on most Carolina Sport Fishermen is there to hold the bow high and keep the highly warped forefoot clear of the water as well as lessening the very sharp bow plunging deeply into waves. Holding the highly warped bottom bow sections clear of the water would lessen the tendency to develop the suction Blount attributes the "non oscillatory instability" to.

Perhaps there are two ways to look at the well. One is that the well is formed by an extension of the hull which seems to be how you're looking at it. Compared to a shorter hull without a well the well probably wouldn't cause any more ventilation of the bottom ahead of the well.

The other is that the well is cut into the hull without changing the length which is how I was looking at it. In that case the well would be a source of air for ventialation of the aft portion of the bottom.

The Simmons Sea Skiffs don't have a highly warped forefoot. Rather the deadrise looks to stay about constant forward with no warp in the bottom. The chines and keel intersect at the bottom of the stem.

[tom28571]

Originally Posted by DCockey

Perhaps there are two ways to look at the well. One is that the well is formed by an extension of the hull which seems to be how you're looking at it. Compared to a shorter hull without a well the well probably wouldn't cause any more ventilation of the bottom ahead of the well.

The other is that the well is cut into the hull without changing the length which is how I was looking at it. In that case the well would be a source of air for ventialation of the aft portion of the bottom.

The Simmons Sea Skiffs don't have a highly warped forefoot. Rather the deadrise looks to stay about constant forward with no warp in the bottom. The chines and keel intersect at the bottom of the stem.

I don't see how the way we look at the boat changes anything but I agree that the propwash might ventilate the inside "sponson" in a turn but probably not running straight. I had a well boat for several years and never noticed any ventilation like that.

Yes, the deadrise does not change much forward on a Simmons. Notice though that the topsides do have serious curvature there, down low. That is what I blamed the chine riding I found in power dories on. Once she went over at speed, the suction created by the convex side held it there until power was cut and the suction dropped. If you search the C Dory owners forum you will find that others have experienced the same issue.

I think it is an issue with power dories.