Larger ST21 Plans

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serge
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Larger ST21 Plans

Post by serge »

Hello,

The ST21 checks a lot of the boxes for my do it all boat.

But a bit longer and wider would be better for my needs.

I am not sure if it is feasible.

General ideas:

25' long
6.5' beam
Diesel inboard
12" draft w/ 1200 lbs of people and gear
Fully protected prop and rudder
17 mph cruise

Any plans in the works that come close?

Thanks and look forward to the response.

Serge

TomW1
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Re: Larger ST21 Plans

Post by TomW1 »

serge wrote: Sat Aug 21, 2021 11:38 am Hello,

The ST21 checks a lot of the boxes for my do it all boat.

But a bit longer and wider would be better for my needs.

I am not sure if it is feasible.

General ideas:

25' long
6.5' beam
Diesel inboard
12" draft w/ 1200 lbs of people and gear
Fully protected prop and rudder
17 mph cruise

Any plans in the works that come close?

Thanks and look forward to the response.

Serge
Hi Serge and welcome to the forum. Jacques usually limits the stretching of his designs to 10%, this would mean about 24' by 6' 4". A diesel engine is standard. Draft at 2000lbs is 9" so your good there. The prop and rudder are protected in the tunnel. Projected cruise is 12-18mph.

Wait for Jacques to answer on the stretching on this boat though as it is a specialty boat.

Tom
Restored Mirror Dinghy, Bought OD18 built by CL, Westlawn School of Yacht Design courses. LT US Navy 1970-1978

serge
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Re: Larger ST21 Plans

Post by serge »

Thanks for the reply Tom.

I'm not really asking about me personally stretching the existing plans by 10%.

The study plans clearly state not to ask about increasing beam.

The plans themselves have way too many different pieces on the hull with intricate shapes I have no desire to try and modify.

In an ideal world BoatBuilder comes back and says yes we've been thinking about that and here it is.

New bigger plans with the kit purchase option.

I doubt that's the case but it doesn't hurt to ask.

Thanks again and look forward to seeing an answer.

Serge
Last edited by serge on Tue Aug 24, 2021 9:04 am, edited 1 time in total.

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BarraMan
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Re: Larger ST21 Plans

Post by BarraMan »

serge wrote: Sun Aug 22, 2021 2:34 pmThanks for the reply Tom.
I'm not really asking about me personally stretching the existing plans by 10%.
The study plans clearly state not to ask about increasing beam.
The plans themselves have way too many different pieces on the hull with intricate shapes I have no desire to try and modify.
In an ideal world BoatBuilder comes back and says yes we've been thinking about that and here it is.
New bigger plans with the kit purchase option.
I doubt that's the case but it doesn't hurt to ask.
Thanks again and look forward to seeing an answer.
Troy
Scaling up the plans by 10% is not difficult. Buy the metric plans and multiply all the measurements by 1.1 and write the new figures in brackets beside the old ones. It probably does mean that you have to cut the panels yourself, but that is not difficult either. Then you just put it together as per the plans. The nesting, as per the plans, will not work so you probably will need a couple of extra sheets of ply.

Will work just fine with a complicated hull like the ST21. If I wanted a larger version of the ST21 I would not hesitate to upscale 10%. Jacques will advise on whether extra glass laminations are required.

But remember that its easy to say, "I'll upscale by 10%", but doing so will turn an already large boat into a substantially LARGER boat! How do I know? Cause I did just that with the Mangusta hull and turned a 20' boat into a 22' boat = more ply, epoxy, glass, paint, trailer, $$ etc!

Do I regret my decision to do so - NO, not for a second! I got the boat I wanted and it has exceeded my expectations in every way!

serge
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Re: Larger ST21 Plans

Post by serge »

Thanks for the reply Barra.

The way you outline it doesn't seem too difficult.

I'll wait and see what the designer has to say before making a decision.

Serge

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Re: Larger ST21 Plans

Post by jacquesmm »

I didn't realize you were waiting for my approval.
10% scaling is very possible and easy. If you scale up, there will be no weight or volume problems.
You can use the same specifications.

The problem with the beam is the tunnel: you can't just increase the beam but you can scale the whole design up keeping the proportions.
Jacques Mertens - Designer
http://boatbuildercentral.com

serge
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Re: Larger ST21 Plans

Post by serge »

Thanks for the confirmation Jacques.

Before I committed to a bunch of hours and dollars I'd like professional confirmation that it was feasible and not a hair brained idea.

And that nothing needed changed in material types, thicknesses or amounts from the original plans.

I'll be sure to start a build thread if I pull the trigger.

Serge

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VT_Jeff
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Re: Larger ST21 Plans

Post by VT_Jeff »

If scaling, use metric, and dont scale the transom height. 8O

Good luck!
There are only two seasons in Vermont: boating season, and boat-building season.

Completed Paul Butler 14' Clark Fork Drifter
Completed Jacques Mertens FS14LS + 10%, Build Thread
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Fuzz
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Re: Larger ST21 Plans

Post by Fuzz »

VT_Jeff wrote: Tue Aug 24, 2021 2:20 pm If scaling, use metric, and dont scale the transom height. 8O

Good luck!
This being an inboard why would you not scale the transom height also? Understand for an outboard.

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VT_Jeff
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Re: Larger ST21 Plans

Post by VT_Jeff »

Fuzz wrote: Tue Aug 24, 2021 2:29 pm
VT_Jeff wrote: Tue Aug 24, 2021 2:20 pm If scaling, use metric, and dont scale the transom height. 8O

Good luck!
This being an inboard why would you not scale the transom height also? Understand for an outboard.
Nope, you're right. Read that about the inboard but it didnt compute, good catch!
There are only two seasons in Vermont: boating season, and boat-building season.

Completed Paul Butler 14' Clark Fork Drifter
Completed Jacques Mertens FS14LS + 10%, Build Thread
Started Iain Oughtred Tammie Norrie

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