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Posted
On 2/27/2024 at 9:05 AM, Chick Ludwig said:

It will stick it's nose in the air and "mush" along. Or if it does plane, it will porpoise badly.

What makes you say that? It doesn't look like there is much rocker in the bottom surface. Although it is hard to tell from photos. Attached is one from Paul356's build. 

 

I see Chespearl asked about adding a motor to a CS17 in September of last year. Graham's calculation was 10.3 knots with a 10hp at 600#. The the caveat that it is hump speed so it could vary greatly. 

 

I think a small wedge, interceptor, or trim tab could fix the bow high issue, and I wouldn't plan to run the boat at very high speeds. 14-18knots would be great. 

 

Seems silly to modify a sailing hull to use a motor with when there are so many planning hulls available, but I like the lines of the CS17 and there are a lot more of those used for sale than there are Outerbanks 20's. Compared the the "downeast" boats that are sold today with similar lines the CS17 would be way cheaper. 

 

What I really want is a 25 Frost Redwing/Thorobred with a small house. Something to rival the Aroha 29. But I don't have the time or money to make that happen. So I sit here and pontificate. 

post-1405-0-93516200-1437958967.jpg

  • 4 months later...
Posted

Two issues that I see.

 

1.The strength of the transom and its connection to the hull

2. The rocker in the hull will fight against planing, not sure what the result will be when it tries.

  • 4 weeks later...
Posted
On 7/13/2024 at 8:50 PM, Don Silsbe said:

Have you considered a Jessy 17?

I'm not a big fan of flat bottoms. 

 

On 7/13/2024 at 9:06 AM, Hirilonde said:

Two issues that I see.

 

1.The strength of the transom and its connection to the hull

2. The rocker in the hull will fight against planing, not sure what the result will be when it tries.

Agreed. The transom would need to be reinforced. 

 

Do you think there is that much rocker? It doesn't look like it from the photos. 

 

Posted

I agree with you about flat-bottom boats.  They pound when hitting waves.  I thought the Jessy had a V-hull entry with a small amount of deadrise at the transom.  This photo of a Jessy 17 showing that it has a V-hull, not a flat bottom.IMG_2667.thumb.jpeg.00f4ffbd93bcca6ba43ede36178728df.jpeg  The specs state that this angle is 10 degrees. The main difference between a powerboat and a sailboat hull is the lack of rocker aft of center on a powerboat.  Ideally, on a powerboat, it goes straight back.  Draw a straight line along the bottom, from the mizzen going aft.IMG_1745.thumb.jpeg.c7a64b5d1a2a5aa7791e2d8bcf473e9d.jpeg  This line, or a little deeper at the transom, would be your resulting elevation of the bow.  It would be deeper at the transom because of the weight of the motor and skipper, and also the less buoyancy of the deadrise at the transom.   I believe that one of the reasons Graham and Allen have shown a center console is to move the skipper’s weight forward.  I suggest digging a little deeper into the Jessy, and also borrowing a 10 or 15, and slapping it on the transom of your CS17. Armchair discussions are only worth so much, especially when our minds are made up on the subject.    

Posted

Don's got it! The planing bottom boat has no rocker in the aft and center hull bottom. The location of the center of gravity in relation to the center of the planing area is important for proper planing. That is why the console is forward. As for deadrise, the boat with no deadrise requires less power to plane it. But, that is not the only consideration in most cases. As Don said, it will pound in choppy water. The more deadrise you have, the less it will pound, but the more power you will need. A prime example of this is the deep-V design power boats as designed by C. Raymond Hunt back in the 50s~60s.

  • Like 1
Posted
On 8/6/2024 at 9:00 AM, Chick Ludwig said:

Don's got it! The planing bottom boat has no rocker in the aft and center hull bottom. The location of the center of gravity in relation to the center of the planing area is important for proper planing. That is why the console is forward. As for deadrise, the boat with no deadrise requires less power to plane it. But, that is not the only consideration in most cases. As Don said, it will pound in choppy water. The more deadrise you have, the less it will pound, but the more power you will need. A prime example of this is the deep-V design power boats as designed by C. Raymond Hunt back in the 50s~60s.

We are all in agreement that powerboats have less rocker than sailboats. I am failing to see that Jessy 17 has less rocker than CS17. Does anyone have any proof of this? Also, for further clarification, rocker is curvature. A buttock that is angled to the waterline is not rocker. The hull will rotate bow up when it planes, but will have no issues with planning. 

On 8/5/2024 at 10:17 AM, Don Silsbe said:

I agree with you about flat-bottom boats.  They pound when hitting waves.  I thought the Jessy had a V-hull entry with a small amount of deadrise at the transom.  This photo of a Jessy 17 showing that it has a V-hull, not a flat bottom. The specs state that this angle is 10 degrees. 

 

I didn't realize Jessy had deadrise. There is not a lot of warp in the bottom so the deadrise is pretty flat towards the bow and the photo I was looking at was from above and it looked like a flat bottom. But thank you for pointing this out. 

  • Like 1

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