Stretch a Coronado

Questions about modifying a design

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Stretch a Coronado

Postby Radioactive » Sat Jul 21, 2007 12:58 pm

I have recently purchased the plans for the "Coronado".

It was always my intent to "stretch" the boat a bit. The section of the instructions titled, "Varying Boat length" on pg 2, reads:

"Alternately, the boat length can be increased by adding a duplicate Frame #1 at the same spacing shown - a stronger arangement that will add 2' 9" to the overall length. When this is done some minor refairing of the frames neasest the transom may be required to maintain the true lines at the sheer and carlin"

It is that last part that is somewhat confusing. I have always thought ( perhaps incorrectly ) that fairing invloved the removal of material. In this case, it appears that it would be necessary to increase the size of frames aft of frame 4. Or does it indicate that the "new" frame one ( for this discussion, labeled 1a ), aftmost, is to be reduced in size ( and the transom resized ) to achieve fair surfaces.

At first look, it would seem that adding material to frames 2 and 3 would be more work, but on reflection, re-designing the transom looks to be a bit of a bother.

Which choice was the intent of the designer?

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Re: Stretch a Coronado

Postby greyrfox » Tue Nov 27, 2012 8:54 pm

Too bad no one took this question and tried to answer it. I too am planning on building a Coronado and stretching it the full length allowed and would also like to know what is meant by the instructions? (given that Radioactive was accurately quoting the instructions word for word.???) Any response from anyone out there would be greatly appreciated. It does look like the transom needs to be smaller if all you do is add a duplicate frame #1. It would also seem that the notching for the battens would have to be deeper as well to keep the curve of the sides fair and true and I have a problem visualizing that that would be the case???? Anybody???


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Re: Stretch a Coronado

Postby drguyor » Tue Aug 08, 2017 3:15 pm

5 years between posts, and 5 years till now. I guess it's time to add to the discussion.

I'm looking at the Coronado Study Plans and it states on Page 2,
Boat length can be varied... respacing frames proportionately and/or adding a duplicate frame aft. I see how adding an additional frame would be good for strength. Does this frame need to be Frame #1? I'm looking at the Coronado strictly for the hull, there will be another set of plans to build the cabin. That being said, is it possible to set another Frame 4 in place of Frame 3 and push everything else aft? Frames 3, 4, and 5 seem to be the most linear parallel to the CL, and you shouldn't need to take much of the new frame (call it 3a?) to make it fair.

My method of lengthening the hull will be to respace the frames and refair the hull. I'm not looking for the full 28'-3", I just want to extend the cabin bulkheads and gain a little more space on the back deck.

I'm not looking to run fast, just enough to get up on plane in the Great Lakes, so the additional frame will only be more weight for me. I'm also thinking of turning the engine around to install a V-Drive. I just like the clean lines of an inboard on a cruiser.

It's been 5 years. Radioactive, greyfox, have either of you built this yet? I'd be interested on which way you went with your build.

- Dan

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Re: Stretch a Coronado

Postby hoodman » Tue Aug 08, 2017 5:30 pm


I would say if the plans suggest a specific frame to duplicate to go with that. It's hard to anticipate what deviating from the plans will do on down the road. Seems to me on most boats duplicating frame 1 and fairing it in would be much easier than any of the ones further forward. I think the way I would do it is to build all the frames per plans and lay them out on the building form in the stretched configuration. Then if you decided you wanted the additional frame, that would be the time to add it. At that point you would be better able to figure out what fairing would be needed (or if you needed to build it slightly oversized. Do the plans indicate that the extra frame is optional?

I would think going from the I/O drive to a v-drive is reasonable since you're not changing the location of the weight of the engine.

What are your plans for the topsides. Hope you decide to go forward with building a boat. It's a lot of fun!

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Re: Stretch a Coronado

Postby galamb » Tue Aug 08, 2017 7:22 pm

Since it states to duplicate frame 1 you can be sure the designer "knows" this will work.

I stretched my last build by adding an additional frame (also frame one - different boat however/Cuddy Sport). In that design the hull was quite straight between the transom and frame 2, so simply adding another frame in between didn't require any additional fairing - at least none I had to scratch my head about, it was simply an extra 20 some inches of boat, at the aft end...

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Re: Stretch a Coronado

Postby Nova SS » Wed Aug 09, 2017 5:10 am

My suggestion would be to call/email Glen-L themselves. Either that or stick with what the plans say. That way you are guaranteed the kind of results you are hoping for. I would hope that Radioactive or Greyfox have done this since so much time has elapsed since they first tried getting an answer on the forum. The Coronado looks like a great design I'd love to see someone build one.

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Re: Stretch a Coronado

Postby drguyor » Thu Aug 10, 2017 2:06 pm

Thanks for your input, Matt. Stretching seems like the better option than adding if for no other reason than that it's easier.

I haven't bought the full plans, just the study plans for now. I definitely want the Coronado hull but I wanted more of a live-aboard cruiser than a sport fisher, and something trailer-able. I really like the lines of the late 60's Chris-Craft Constellation my father-in-law used to own, so I'm thinking of putting the Islander cabin in the Coronado hull with a hard-top over the helm.

Much as I love the idea of a fly-bridge, I also ride a motorcycle and like to be out of the weather when it rains. Adding a second helm like the Phantom has is a little out of my price range. That takes me back to the Islander, but with a hard-top over the helm.

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