Yet another "scaled CS25?" thread

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Christer
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Yet another "scaled CS25?" thread

Post by Christer » Sun Oct 01, 2017 1:59 pm

Hi,

I hate to bring this dead horse back to life yet again, but after reading most, if not all the threads regarding scaling the CS25 to 27-28ft and Jacques repeatedly saying "max 10%", I have come to terms with the fact that I can scale the CS25 to 27.5ft, which with an engine bracket would bring the boat's length to 30.5ft total. And that's perfect!

However, I have a few questions regarding this:

1. Does this scaling dramatically change the behaviour, seaworthiness and predictability of the boat? Jacques has mentioned on several occasions that it really should be a new design.
2. If I scale it 10%, I guess I would have to cut every panel myself from my upscaled measurements. Would assistance in calculating a new BOM be available?
3. Would it be possible to add the extra 2.5ft to the aft section of the boat? I really like the looks and the lines of it as it is, however I feel the rear part is slightly too short and would like it a little longer. This way, the front section down to where the curved foredeck meets the straight gunwales of the rear part would stay the same length as in the original plans and the rear section would be extended by 2.5ft in length, plus whatever the width would be when scaled.
4. Should I just stick to the original 25ft plans, get a CNC kit and a 3' bracket and call it a day? I'm not even sure I need a 25' boat, let alone a 27.5' one... (but I just really, really, really want one, because then I could build a jump cabin version with a head and some basic amenities and not lose too much of the casting deck.).

If I'm off my rocker on this one, please don't hesitate to tell me so. I'm so early in the planning stages of this build that I'm currently planning to get the plans at some point, let alone getting any build materials.


8ft dinghy built in 1992, BBV sufferer ever since.

PNWcx25
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Re: Yet another "scaled CS25?" thread

Post by PNWcx25 » Sun Oct 01, 2017 5:08 pm

Christer wrote:
Sun Oct 01, 2017 1:59 pm


2. If I scale it 10%, I guess I would have to cut every panel myself from my upscaled measurements.

You or Jacques could have a find a CNC large enough to do it if Jacques is not large enough, but of course there always an extra fee. I upscaled my build 9% because I could not find a sheet for the transom larger than 1219 X 2438 mm. My thinking is that for the extra 80mm sheet or so needed to upscale to 10% would require far more skill and work than I was willing to give. So far each frame is taking about an extra 1/2 hour to upscale - it's just part of the fun.

By the way I've cut everything myself with very little experience

Would assistance in calculating a new BOM be available?

I'm afraid to look - shouldn't be to difficult



If I'm off my rocker on this one, please don't hesitate to tell me so.

Maybe not but I seem to be so why not join the club. Good luck with your decision


Tony

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Re: Yet another "scaled CS25?" thread

Post by Christer » Sun Oct 01, 2017 7:17 pm

Thanks for your comments.

I had a long, hard think about this project today and realized that I may have overthought things quite a bit.

I currently have a 15 foot open boat powered by a 30HP outboard. This boat is just slightly too small for what we use it for - small, short outings, some fishing in protected waters and some medium long trips when the weather's nice (which it rarely is).

Ideally, the boat really only needs 2-3 extra feet of length to be perfectly suited for what we currently use it for. However, I want to be able to drive up the coast for 4-5 hours without getting too cold or wet, or go fishing further out towards the North Sea. For that, we need a bigger and safer boat. Out there, seas are rough and waves can be quite tall. I'm not going offshore fishing with the family when the weather's in kill mode, but things change fast around these parts and hence a reliable boat that will get us back home fast and safely is required. My fiancee would probably argue that we just don't go out there in the first place, but I'm not listening to her trying to ruin my (utopian) dream of building a fantastic boat, with her logic and reasoning.

So, while out on the open sea, someone needs to go, so obviously I need to install a head. Which should ideally be under some sort of deck. Not sure if I would need beds or even standing height, but a place to sit down and have a bit to eat and a cuppa would be nice and also allow us to take longer trips. An added bonus is a lockable storage room when moored.

I can't really appreciate the size of the CS25, but I always thought the jump cabin version seemed to have a quite small deck area and maybe even a little cramped at the back - hence my thinking that an upscaled CS25 to 27.5ft would be perfect, as I could then build the jump cabin version and still have lots of room on deck.

Anyway, while I was thinking about it today I realized that an unmodified CS25 is 10 feet longer than my current boat, and that 10 feet is 3 meters. My current boat is 4.5 meters. Scaling it to 27.5ft and then attaching a 3ft bracket would double the length of my current boat, which is then quiiite a bit more than what I actually need. Then again, needs and wants are rarely in line...

I've read Peter-from-Curacao's build thread and really liked his build. I've also watched Walkers Run's video and read his build thread; unfortunately the pictures are missing thanks to PhotoBucket's brilliant policy change wrt 3rd party hosting; many good ideas there as well. Then this sketch came up in a thread:

Image

It seems to have a larger front deck than the jump cabin version, which obviously shortens the aft deck, which is where the CS27.5 comes into plan, especially if the extra length can be added onto the rear part of the boat and leave the front lengthwise dimensions as-is.

Ultimately this build won't start for at least another year, so I'm hoping that Jacques will incorporate the above cabin design in the plans and/or design a 27-28ft version of the CS. It would save me a lot of work and probably trouble having official plans for a boat that size (as well as a CNC kit :)).

Man, I'm ranting.
8ft dinghy built in 1992, BBV sufferer ever since.

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Re: Yet another "scaled CS25?" thread

Post by Fuzz » Sun Oct 01, 2017 8:54 pm

Maybe look around and go onboard a few different boats of the size you think you are looking for first. Boats grow really fast. If your 15 foot boat is 5 wide and it was square it would be 75 square foot. 25 X 8 equals 200 square foot. 28 X 9 equals 252 square foot. As you see by adding 3 feet of length and one foot of beam you get a 25% larger boat. I am betting a C21 like Eric is building would seem huge to you. And the DE-23 would cover your wants very nicely. Just my opinion :lol:

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Re: Yet another "scaled CS25?" thread

Post by Eric1 » Sun Oct 01, 2017 9:17 pm

Fuzz wrote:
Sun Oct 01, 2017 8:54 pm
Maybe look around and go onboard a few different boats of the size you think you are looking for first. Boats grow really fast. If your 15 foot boat is 5 wide and it was square it would be 75 square foot. 25 X 8 equals 200 square foot. 28 X 9 equals 252 square foot. As you see by adding 3 feet of length and one foot of beam you get a 25% larger boat. I am betting a C21 like Eric is building would seem huge to you. And the DE-23 would cover your wants very nicely. Just my opinion :lol:
It sure seems big to me! :lol:

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Re: Yet another "scaled CS25?" thread

Post by Fuzz » Sun Oct 01, 2017 9:21 pm

Eric that is because you took a 21 foot tree and sanded into a boat shape :lol: :wink:

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Re: Yet another "scaled CS25?" thread

Post by Eric1 » Sun Oct 01, 2017 9:29 pm

Fuzz wrote:
Sun Oct 01, 2017 9:21 pm
Eric that is because you took a 21 foot tree and sanded into a boat shape :lol: :wink:
That's funny right there. :lol:

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Re: Yet another "scaled CS25?" thread

Post by BarraMan » Mon Oct 02, 2017 4:37 am

However, I have a few questions regarding this:
1. Does this scaling dramatically change the behaviour, seaworthiness and predictability of the boat? Jacques has mentioned on several occasions that it really should be a new design.
You won't know until you build it and put it on the water. I messed around with my boat quite a bit from the plans, but accepted the risk that it would have negative consequences. In my case it all worked out fine and I love the boat.
2. If I scale it 10%, I guess I would have to cut every panel myself from my upscaled measurements. Would assistance in calculating a new BOM be available?
I suspect that you are on your own with this - I was. I think the rule of thumb is, increasing the lengths by 10% will increase the area by 20% and the volume by 30%. I had to order new sheets of ply as required as I couldn't really work out a good nesting plan.
3. Would it be possible to add the extra 2.5ft to the aft section of the boat? I really like the looks and the lines of it as it is, however I feel the rear part is slightly too short and would like it a little longer. This way, the front section down to where the curved foredeck meets the straight gunwales of the rear part would stay the same length as in the original plans and the rear section would be extended by 2.5ft in length, plus whatever the width would be when scaled.
This is way out of my league! Very risky without the input of a naval architect IMO.
4. Should I just stick to the original 25ft plans, get a CNC kit and a 3' bracket and call it a day? I'm not even sure I need a 25' boat, let alone a 27.5' one... (but I just really, really, really want one, because then I could build a jump cabin version with a head and some basic amenities and not lose too much of the casting deck.).
That seems like a good idea to me. Its really easy to say, "I'll upscale it by 10%", but the reality is that you will end up with a much bigger boat than you might have expected. How do I know????

I luv my boat - but it is BIG. A 10% upscale turning it from a 20 footer to a 22 footer and taking the width to just less than what is legal in Oz.

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Re: Yet another "scaled CS25?" thread

Post by TomW1 » Mon Oct 02, 2017 2:48 pm

Christer have you looked hard at the CS25 it gives you a much larger rear deck with the bracket. It gives you the toilet space and a place to lie down or sit and shoot the bs. I say lie down cause if they get sea sick the last thing they want to do is be standing up. :lol: It also places you higher for spotting birds which indicates schools of fish, at least over here they do. It also has a refrigerator, stove, storage drawers and sink which you may not want but you can leave out and replace with a large cooler. Just food for thought.

Good to see another Norwegian builder with us.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses.

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Re: Yet another "scaled CS25?" thread

Post by Christer » Thu Oct 05, 2017 12:57 pm

BarraMan wrote:
Mon Oct 02, 2017 4:37 am
However, I have a few questions regarding this:
1. Does this scaling dramatically change the behaviour, seaworthiness and predictability of the boat? Jacques has mentioned on several occasions that it really should be a new design.
You won't know until you build it and put it on the water. I messed around with my boat quite a bit from the plans, but accepted the risk that it would have negative consequences. In my case it all worked out fine and I love the boat.
2. If I scale it 10%, I guess I would have to cut every panel myself from my upscaled measurements. Would assistance in calculating a new BOM be available?
I suspect that you are on your own with this - I was. I think the rule of thumb is, increasing the lengths by 10% will increase the area by 20% and the volume by 30%. I had to order new sheets of ply as required as I couldn't really work out a good nesting plan.
3. Would it be possible to add the extra 2.5ft to the aft section of the boat? I really like the looks and the lines of it as it is, however I feel the rear part is slightly too short and would like it a little longer. This way, the front section down to where the curved foredeck meets the straight gunwales of the rear part would stay the same length as in the original plans and the rear section would be extended by 2.5ft in length, plus whatever the width would be when scaled.
This is way out of my league! Very risky without the input of a naval architect IMO.
4. Should I just stick to the original 25ft plans, get a CNC kit and a 3' bracket and call it a day? I'm not even sure I need a 25' boat, let alone a 27.5' one... (but I just really, really, really want one, because then I could build a jump cabin version with a head and some basic amenities and not lose too much of the casting deck.).
That seems like a good idea to me. Its really easy to say, "I'll upscale it by 10%", but the reality is that you will end up with a much bigger boat than you might have expected. How do I know????

I luv my boat - but it is BIG. A 10% upscale turning it from a 20 footer to a 22 footer and taking the width to just less than what is legal in Oz.
I sketched up the general dimensions of the boat in the driveway and well into the carport the other day (sorry, no pics, the rain killed the drawing withing minutes), and I've come to the conclusion that a "regular", built-to-plans CS/CX25 is more than enough boat for our needs. It's enormous!

Built with the jump cabin and a head, a small fridge and a place to get out of the weather, a windshield and a clear button top under a T-top like in the picture I shamelessly stole above, it will have plenty of aft deck space and space in general.

My mind is set, now I need to start saving for the materials.
8ft dinghy built in 1992, BBV sufferer ever since.

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