Yet another "scaled CS25?" thread

[Bhill]

Jacques,

with the scaling up of the CS25 (CS 28) using a bracket what is the max twin set up we can expect it to support? would twin Suzuki 325's be doable for example?

iv been lurking on these builds for some time now and love the design and am extremely excited about the possibility's of a CS 28!

[TomW1]

Scaling to 28' would be excessive for the CS25. The max would be 10% or 27.5. Just for your information this boat was designed from a 24' design and then the CS23 and CS25 were the result of that of original design. Twin Suzuki 325 will totally over power the boat you want to build. These boats are much lighter than any fiber glass boat. One builder put a 300 Evinrude on his built as designed CS25 and had top speeds in the 40's. You need to look at the weight on the transom before selecting the motors. At 27-28' you can run twin 250 HP motors or a total of 500HP and the weight would be acceptable with some additional build up of the transom. You may also need to add an extra layer of fiberglass to the bottom of the boat do to the additional speed you will attain
'
Please wait for Jaques Mertens the designer to reply. He is the final say on what you can and can't do.

Tom

[Bhill]

yeah like I said iv been researching this boat on the forum for a long time and watching the builds I just used the term CS28 because that's what it was referred to as on this thread a few months ago. Yes this would be lighter than a solid glass hull but there is a lot of sandwich cores in this size range pushing some big HP #'s and the 325's just seem like it has some really interesting features to me (v6,runs regular gas, has counter rotating props). I totally agree even twin 200s would probably get the job done but being form Texas "bigger is better" haha. The weight difference compared to the 250AP twins would be 177lb which doesn't seem like a lot to me. Just wanting to spit ball the max capabilities of what to expect from the scaling.

[TomTom]

I can’t help but think you would be better off and more likely to complete this project with the GS 28 hull .... I know there are huge differences between them but it’s a more manageable project and would be much more efficient to power, and (arguably I know) not give much away from a safety/ seaworthiness aspect for the conditions you describe.

[jacquesmm]

The GS28 is a good suggestion but it is a narrower hull with a little less freeboard. It should not be fitted with that much HP and I have the feeling that what drives this project is HP.
The 10% scaling rule is not absolute. For the hull shape, scaling a CS25 to 28 is feasible but a lot of other specifications must be changed especially if the goal is too use that much HP. With the current scantlings, as TomW1 says, the bottom will fail.
It's not the transom that I am worried about, it's the whole structure: the bottom must be made much stronger, the framing must be stronger = lots of changes.
That is why I recommend not to scale more than 10% unless you recalculate all those those components.
A 28 will be heavier and will go faster. The slamming loads on the bottom are a direct function of the weight and a square function of the speed. Increase the speed by 20% means a 44% increase of the bottom pressure. Add the increase of the weight and you'll get a total increase of more than 70%, all that with more frames.
I don't have to redesign the hull, she will float right and run well but we have to add frames and seriously increase the bottom specs.

How about I supply lines for a 28' hull with new specs, new stations and the location of the LCG? Nothing else, no renderings, no drawings of cockpit and deck, just a good hull and specs.
I can do that easily but want to charge an honest fee for it. At least twice the price of the current plans.
The specs would be for foam sandwich, Corecell and SilverTip resin.

[TomW1]

That sounds like a fair deal Jacques. Tom

[TomTom]

Sounds like a no brainer of a deal to me! I think Jacques is mellowing as he gets older...