Changing a design

[John Stevens]

Hi,

I'm going to be building a Minuet 15 foot. This would be the "perfect" boat for me if it was around 13 feet. I would think that I could scale everything down to 13 feet. If I change the mast and keel location in the same scale wouldn't it stay relative and still work well? Any thoughts?

TIA,

John

[wkisting]

John,

It is certainly possible to scale down a design, but it can be tricky business if you're not very aware of how the factors change and affect each other. There are some very experienced folks here who could probably guide you through the heavy-thinking part, but it will also probably take some experimentation on the practical end to balance the boat properly afterward.

I know this isn't what you asked but: Are you talking about the Glen-L Minuet? (Just curious) If it's a matter of shrinking from 15 feet to 13 feet, I wonder why you would want to do this. It may be you're working in very tight space constraints or something like that, but I would strongly encourage you not to modify the plan in this manner. There are several reasons why, but here's the main few I would encourage you to consider...

Although you're only proposing shrinking the boat by 2 feet, I think you would be surprised just how much "smaller" even a slight reduction like this can make the boat seem. To keep the proper lines and same beam-to-length ratio as the original plan, you'd have to scale down the beam (width) in the same proportion, so your space, displacement, buoyancy, etc. are going to decrease noticeably. So, too, is your sail carrying power and stability... at least to some extent... unless the original design is way underpowered or overballasted to begin with.

A 15' boat is already quite small (I have a 14' Stevenson Pocket Cruiser myself) and I can say with quite a bit of confidence that even if it seems bigger than you need at present, you'll be glad you didn't shrink it once it's built. Space is tight, at best...

Besides that, if you're talking the Glen-L Minuet which (I think) has a cabin, it's also going to be a heavier boat for its size (compared to an open dinghy, etc.), and really, I think the cabin-style "pocket cruiser" type boats are somewhat impractical for sailing in some ways. That's not to criticize the type, only to say that they already have some limitations which any effort at scaling-down may exacerbate.

My Stevenson PC sails well, but not nearly as well in light airs as a lighter, more open boat would, nor as well as a cabin boat with a longer waterline (to handle the weight better) probably would... I consistently find myself wishing she were either cabin-less (to give more space and reduce weight) or larger (to carry more sail and manage the weight issue better) so that she wouldn't be as finnicky about how weight is distributed and whta points of sail she can hold.... and so she could perform better in light airs.

Not trying to give you the idea she's a bad sailor--she isn't--but her size brings her own hassles and compromises, much like the 15' boat you're proposing would. The reason I built her, though, was because 14' was pretty much the largest I could build in the space I had available at the time... chose the cabin style sharpie because I built her for my honeymoon and needed sleeping accommodations (see http://www.roguepaddler.com/boat.htm for the pics & story if you're interested.) Turned out terrific for our needs.

Not trying to sugges the Minuet isn't worth building. That's not what I'm saying at all. I've never regretted our PC and she brings us much enjoyment. What I'm saying is that taking a boat that is already small and making it smaller may only increase the logistical hassles and compromises that are already inherent in the original design... (really, in virtually any cabin-style boat in this size range, which though impractical, also brings its own charm and joys, too).

Of course, if you're talking about a different design called "Minuet", none of this may apply. If it's an open boat, open boats do lend themselves to modification much easier than "pocket cruisers", in my opinion, though there will still be trade-offs.

[Guest Oyster]

Hi' date='

I'm going to be building a Minuet 15 foot. This would be the "perfect" boat for me if it was around 13 feet. I would think that I could scale everything down to 13 feet. If I change the mast and keel location in the same scale wouldn't it stay relative and still work well? Any thoughts?

TIA,

John[/quote']

The big word of the day is "if" when discussing a perfect design for you. If you have to modify something, then its not the perfect design, if you are indeed thinking about changing someone elses plans. I do not support the idea that people, with only the capacity to purchase plans, and not to design and sell plans and all the liability issues and in some cases the potential disasters that goes with folks doing this can just scale something up or down and make it act and work the same as originally drawn up.

Its hard enough to even make prototype plans work properly, to fit the numbers, and in many cases, some modifcations are done after some time and hulls are built to improve the actual original ones. So keep looking would be my .02 worth.

[John Stevens]

Yes it's the Minuet by Glen L.

Reasons: I currently own a Precision 18. It's a nice boat but the setup is just a little more than I want for a daysail. I overnight a few times a year in it and it does the job but I'd like something bigger for that in the future. I built an 8 foot pram two years ago and loved building it. It also is a nice boat but too small for my wife and I to play around in, really good for one person. So in the long run I'll be buying something in the 22-25 range but would like a small boat for daysailing more than just one person. I'd also like to be able to spend the night once in a while and get out of a surprise rain here in FL. The Minuet fits the bill but if it were 2 feet smaller and lighter it would be even better and easier to set up.

So again... just wondering if shrinking it down a few feet keeping everything to scale would change the the relationship between the balance of the boat.

TIA,

John Stevens

[Guest Oyster]

So again... just wondering if shrinking it down a few feet keeping everything to scale would change the the relationship between the balance of the boat.

Well, I attempt to say again, that unless anyone here, to be more specific, has done this, or even can speak from real experience of this hull, at all, I think you are asking the wrong group. Hire a good designer if there are no plans on the market that appears to fit your mindset and personal desires for a smaller hull. Why gamble if you are not sure, when the time and steps to build the hull will be the same, for something that is a known commodity? I go out on a limb in almost every case of build lately, but have something to base my alterations on, including past simular hulls and previous exposures to a variety of designs, and still find that each hull carries with it some compromises.

Speaking without any knowledge of your past experience, I still error on the side of caution. Likewise, it would be in your best interest to consult more than just a few short replies from an internet online forum, before venturing off into the unknowns of boat designing, if you personally will be risking your life and your time and money to modify something from the pat on the back of some respondant here. Its always nice to bat ideas around, but spend your money ahead of time with known and experienced folks with those funny letters after their names, before you spend your time with a saw, would be my best advice.

Poke your head around this site for a bit. I bit there is something that would fit your needs in this site in the size requirment.

example.

http://www.duckworksbbs.com/plans/jim/imb2/index.htm

IMB sail beachboat - 13.5x5.5

[Barry Pyeatt]

I will add this to what Oyster has said.

Most designs are not directly scalable, either up or down.

Unfortunately these are not static models that just sit or move about on a solid surface. There are a ton of hydrodynamic factors that have to be coupled with the various forces induced by both wind and water. Consider that you already are talking about a small boat, a really small boat. Now the scale changes but does the loading change by direct scale as well? Wind and water forces may stay relatively linear but when you change a hull to any extent that isn't linear. End result is that it may look the same from a distance, but it won't handle the same in the water with a different ratio of loading.

I used to represent and build a complete line of boats from 12' to 36', some of the smaller designs were scaled in length only but these were work boats with an 8' beam and lots of power. Even then performance suffered with the shorter length. All the ratios changed and nothing remained as a constant. End result was a line of boats that worked well and looked the same except for length, but had to be built with serious modifications to have the different lengths perform well. Glad we wern't dealing wth sail or pleasure. :roll: The demands of the size changes drove our Marine architect about crazy. Lots of tank time to work out the issues and construction requirements.

When you decrease a size it never is proportionally the same if you want it to work as designed. In the vast majority of cases it won't work safely at all.

Just my 2 cents worth. And I know next to nothing about the Munuet 15 other than it performs well for what it is, and it is a successful design. But we don't see direct scaled up or down from there. Doesn't mean it isn't possible but scaling is not just putting it on an enlarged plan or reduction in plan size.

I would contact tthe designer or others that are really experienced with the design before doing anything. And echo getting "OH, just go ahead and do it!" advice on a board or forum. It is your money, your boat and your safety. Not thiers! :wink:

[Guest Oyster]

for your viewing pleasure, another one thats simular in design.

TIDEWAY 14

http://www.selway-fisher.com/PCup16.htm#TIDEWAY

[Barry Pyeatt]

Now that is a cute boat! 8) Selway-Fisher Duette 14'? Isn't the Tideway 14 a similar design, but with plywood construction?

Been enchanted with a number of their designs for quite awhile. 8)

[Charlie Jones]

John- I'll stick a third oar in here against modifying the design. Shrinking or enlarging CAN be done, usually within about a 10% range, but sometimes it's just not simple. I've scaled a couple of boats down in size, but none of them were cabin boats. I really don't think that reducing Minuet from 15 to 13 would give you much of a change in set up, etc. Just a smaller boat.

Another similar boat but a quite simple one you might take a look at is an OLD one- a Sam Rabl "Titmouse". She's a 15 footer also but has a mast in a tabernacle so that is a really simple thing to rig- just stand it up and pin it.

You can look at the design in his book "Boatbuilding in your own Backyard". Out of print I'm sure but interlibrary loan should net you one to look at. You could build from the book, but I think the plans are also available from Duckworks. She's strip built so would be a fairly pretty hull, very close to Minuet.

Or just keep looking a while- there are literally THOUSANDS of small boat plans out there, some very old, some very new, and every thing in between. Find one that suits you WITHOUT modifying the boat size. Modifying interiors, etc, is quite another thing- then you pretty much can do what ever, but build the boat as designed, in hull and rig. You'll be happier with it in the long run.

And you still have my email address I'm sure*grin* Just like last time, I'll be happy to do what I can to assist you.

[wkisting]

John,

I'm sure the last thing you want is another guy telling you what boat to build, but based on what you mentioned for your needs, I have a suggestion I would encourage you to consider seriously.

So in the long run I'll be buying something in the 22-25 range but would like a small boat for daysailing more than just one person. I'd also like to be able to spend the night once in a while and get out of a surprise rain here in FL. The Minuet fits the bill but if it were 2 feet smaller and lighter it would be even better and easier to set up.

If you're sure you're ultimately going to look for a larger boat in the 22' range or so for more than one person (my goal too... I have plans for the B&B Princess Sharpie 22 for my next build), and you're just looking for something for solo daysailing... I'd seriously consider an open boat design like the Core Sound series (B& or John Welsford's Navigator (or a hundred other such designs, though I especially like those two). There are plenty designs around if you're dead-set on sticking to 13-15 feet LOA, and I think Oyster is right that you want to choose the plans that already MEET your requirements, not modify them.

It sounds like your criteria are ease-of-setup, overnight accommodation, and easy-to-manage size... It would be easy to rig most open boats with a tent or soft, fold-up cuddy (many builders have done it). You'd very likely end up with a lighter and better performing boat than any of the cabin-style boats in the size range you're looking at, with decent camp-sailing accomodations for overnight solo trips.... as long as you plan out things carefully when you get around to the rigging and finishing details.

I would've gone that way myself instead of the Pocket Cruiser, but I had a fiancee to think about and didn't want to end up divorced before the honeymoon was over, so needed more than "camp comforts". Even so, aside from the honeymoon, I've never needed the cabin since and, as I said in the previous post, often wished it were an open boat instead for the daysailing it now is used for.

Just my two cents.

[Guest Oyster]

Certain areas that we all live in dictate certain arrangements, if you are afforded the maximum amount of use, both in fixed cabin runabouts and sailboats, and open boats. I still subscribe to the portable dodger-cabin configuation in most smaller hulls, unless you have children under eight years of age that needs a nap or provisions for long days on the water. Graham's arrangement with his dodger is the best of all worlds in a smaller hull, and allows you to make the most use of all the limited areas inside of boats that are 13 to 15 foot.

Heck the Boldger boats, like the Micro Cruiser is still the best and the most simple for building and cabin space.

[John Stevens]

Thank for the all the thoughtful answers. I did talk to the designer and he said they don't advise changing the but changes in the cabin are fine.

I'm sure when I start building it I'll have a million questions.

Thanks,

John

[PAR]

Changing the length of a design has and can be done. Typically this is accomplished by re-spacing the station molds to the percentage of the enlargement or deduction. You're reduction is about 14% and on the very edge of doable. If the station molds only are moved then this will work out, though she will be heavier then she may need to be for her length (15' boat scantlings, etc.)

If you aren't comfortable with literally redrawing the lines (to the new length) then erecting stations molds on the reduced spacing then I'd look for another boat.

Direct scaling down or up doesn't work in boats. There are several reasons for this, you'll just have to trust me, that it tosses all the calculations, on the structure and hull type out the window. Not that you can't have your 13' boat, just that there will be a little reworking of a few areas necessary.

The rig, of course will need to be gone over, though not much effort brain wise. The appendages (center/dagger board, rudder) will need to be resized and probably relocated and the smaller accommodations reworked for humans that haven't been scaled down 14%.

The resulting boat will have a similar charm as the Minuet, but will look just different enough to warrant a new name. She will not have the performance envelope of the Glen-L design, but this boat isn't known for it's sparkling abilities anyway.

Plans for small day boats are plentiful. A 13' boat is very small, especially if you try to include a cabin. It is the smallest of the Glen-L cabin sailors. The Minuet is similar to Weekender in many ways, possibly could be thought of as a "V" bottomed Weekender like boat. She's more stable and has more room then a Weekender, same LWL, LOD, LOA and carries slightly more sail area, having more displacement to drag along. It also costs more to build then the Weekender, takes longer and is more difficult to construct, then Weekender. The Glen-L 12 and 13 are nice little boats, though I wouldn't recommend burdening them with a cabin, when a boom tent will serve just as nicely (and provide full sitting headroom) and they don't carry a bow sprit to increase the space needed in your building area or trailer.

In the end it's your call. The selection of a design is one of the most difficult aspects of building a boat. I've known folks that have taken several years to settle on a design (and been better for it) Make a list of the things you truly must have in the boat, then a list of the things you can live with in a boat. See how much you can discard from the "wish" list to the "find a boat that fits" list.

[Ken_Potts]

I agree that choosing a design is one of the most difficult tasks in building. I've managed to deal with that decision lately only by knowing that I have a sickness and will not stop building. The first boat I built sort of suited my needs then I built another one that suited my requirements a little better. Then I found a new set of requirements...

With a kayak sized project I'm more than happy to build to my own design and take my chances (my first boat = bad, my second = good). with the boat I'm building now (a CS17) I opted to buy the plans and not really vary from them in order to know that the money (and more importantly the time) I'm spending will provide a boat with a specified set of qualities.

I think if you're in it for the building/experimenting experience it will be an interesting project to shrink an already small boat but if you're looking for a good boat the first time it's a good idea to stick with the plans (either course of action is valid).

Whichever route you go, please keep us posted.