Hatteras 36C Series II Keel

[TomT13]

Hello,

I am talking with a mechanic about repowering my 1985 36C Series II. One of the recommendations is to use 8.3 ltr Cummins engines in the 420HP range. This thread isn't really about the engine or the size as there is a great deal of information already on the site relative to that. The mechanic also stated I should cut the keel down to 3" fore to 4" aft from it's current configuration. I was wondering if anyone here has done that and what performance changes were the result doing something that aggressive to the hull. Not sure if the keel is all built up fiberglass or is it filled with anything. Not sure if it is a structural component or if it would affect the prop pockets or not. In all fairness, the mechanic said I should consult a naval architect. Looking forward to substantive responses.

[Cricket]

Why, for "keel walk"? Keel walk does not exist, it's actually suction pulling one side or the other down. Can easily be fixed with the addition of a small batten or similar to the hull to break the suction.

Check out the video, gets into keel walk at 22:50

https://www.youtube.com/watch?v=dirBIsgblt4

[TomT13]

Yes, keel walk at faster speeds. Also to gain some speed as the mechanic seems to think I am losing 4-5 knots.

[krush]

Does your mechanic supplement his day job by moonlighting as a naval architect?

[Bob Bradley]

I imagine that once cut, it would be difficult to "un-cut" if it didn't help, or perhaps made things worse.

[RyanB]

Cant help with your keel question, but just out curiosity, what sort of performance numbers do you expect with those bigger Cummins?

[jim rosenthal]

The 36 Series II boats were not very quick, from new. They had more beam than the earlier 36, Series I, and also more weight, plus a different hull design (one of the few not designed by Hargrave). The diesel boats had mostlyk 6-71s, I think, which are reliable but heavy.

I think you would get all the power you need from Cummins QSB 6.7s, you'll spend less money on engines, and gears, you'll probably be able to use the original shafts or the same thickness, and you'll have more room to work in the engine areas. I would look on the Cummins reman site for a pair of those. I think you'll gain some speed but you aren't going to be near the thirty knot range. And I would NOT cut the keel down, no way. I'd leave that alone.

[rsmith]

The keel is there for a reason. Most of us who love Hatts do because they are great sea boats. The keel helps the boat track in rough conditions and following seas.

[TomT13]

Thank you for the substantive responses. Jim I agree and we discussed the QSB 6.7's as well. I currently have 3208 Cats in the 375 HP configuration. I always thought the boat would be better with a little more power hence the 420HP. I also found Cricket's response informative. I recall seeing that video once before. I would like to talk with Bruce Angel and will attempt to reach him at his new company. If as he stated in that presentation the "leaning" or "keel walk" is a negative pressure gradient set up under the hull that can be corrected with a small batton or strake I will consider that strongly. I do not want to cut the keel either as I understand the benefits and I do not want to modify the hull that dramatically. Thank you for everyone's responses. Have a great day.

[Cricket]

If you end up doing the repower my advice is always the same, buy as much HP as you can afford.
Also, I would run the boat with the new engines before making any hull modifications so you have a baseline to start from so you can go back to if needed. Good luck with it, it's like getting a new boat.