Design Suggestions [Archive] - Boat Design Forums

messman

11-21-2008, 09:54 PM

Ok here is where all of you experienced types get to tell me that I am a fool and what not, but even more important get to give me your suggestions of boat designs that you would suggest. Now please keep in mind I believe in jumping in the deep end or I dont jump in. So here goes.

I am thinking about building a 27' Dory design with a cabin superstructure.

I will be using this craft in mostly bay type areas around the Gulf of Mexico, with limited open water use. It will be used for family outings, fishing, and when the son becomes dive certified, as a diving platform.

Do you all think this would be a good design? or is there another design you would suggest?

Chris

Boatpride

11-22-2008, 03:42 AM

Hi Messman,

reading through your post i got curious about the design so i went hunting and

found an interesting article which should erase any doubts you have about

building your dory. http://ezinearticles.com/?Choosing-

the-Best-Easy-to-Build-Small-Boat-Design&id=951274 (http://ezinearticles.com/?Choosing-the-Best-Easy-to-

Build-Small-Boat-Design&id=951274)

You'll see the dory reference after a few paragraphs. There are several

styles of Dory mentioned and the author of the article is credible.

Hope your son flourishes with his dive certificate.

:)

messman

11-22-2008, 10:15 AM

Boatpride,

Thank you so much for the response. I am glad to see that the choice, in someone elses eyes, appears to be a good one.

The individual who wrote that article, Mr. Spira, seems to be a very nice man willing to help out. I have e-mailed him a couple of times to which he responded quickly. I just wanted to make sure the design I am thinking about is a good choice. You have also calmed some concerns of mine by saying he (Spira) is credible. I have not had the opportunity to research him yet.

I am still very much interested in seeing what design opinions others have, what others recommend I should build.

Chris

Tad

11-22-2008, 03:05 PM

Umm....Mr. Spira is credible because he suggests novice builders should build dories....oh and he also sells dory plans...what luck! :D

Seriously, of course Spria believes in the boats that he has designed. Obviously he cares about the type (dories) and it's use. Dories have their place I'm sure, mainly in the hands of experienced people who need to carry heavy loads in open water. Generally dories have narrow bottoms in comparison to more conventional (modern) vee or multi-chine forms. This means the dory is initially tippy, until the boat has say a ton or so of fish aboard. A tippy boat tends to scare novices...this is not good for family harmony.

MessM you mention a 27' dory, I assume you're thinking of a St. Pierre fishing dory? If so this is a really poor choice for a boat with cabin, they were never intended for this. Again the narrow bottom in combination with high sides and higher cabin makes for a tender (tippy) boat. Something with a typical vee bottom and lower sides will be much better for family use, especially getting a diver on and off.

Also Mr. Spria could improve the safety of his designs tremendously by including a splash well inboard of his transom cutouts. It's very easy for a small wave to come through that low cutout and swamp the boat.

rasorinc

11-22-2008, 03:22 PM

Here is a dory plan with the outboard forward of the transom. you can get an idea of how strong it is built. Stan
https://www.boatdesigns.com/products.asp?dept=277 PS they have cabin layouts for it also

If I had young ones with me out in salt water and getting in and out with diving equip. I would consider a Cat. Here is a link to one that also can have a cabin. There are ones that are trailerable being 8'-6+ wide. Stability is everything with young or old aboard, Just more info for you to consider. https://www.boatdesigns.com/products.asp?dept=781

tom28571

11-22-2008, 03:56 PM

Tad,

While I agree with your arguments, I suspect that you may be pissing against the tide. "Dory" is a word that has reached almost cult status in the novice boating world. There are a couple that have a credible reputation, like the Simmons Skiff of my area that work well for the task that Mr. Simmons set for them. That is, fishing the inshore, inlets and near land ocean waters of the Carolina coast. Kilburn Adams seems to have a workable solution with his Skiff America, which has, as you advise very little cabin structure. The C Dory from your part of the country is very successful is selling all their production although it has some undesirable quirks like you mentioned.

Warning someone off a dory for a cruising powerboat or a sailboat is a little like trying to change their religion. That sweeping sheerline must be a narcotic.

Some, like Renn Tolman have widened the bottom to the point that is is no longer such a tippy dory and have made a well received boat out of it. The older Simmons is also a bit like that and has the open transom well.

Another magic term to go with dory is the double ender although George Calkin has made a great boat for running inlets with one. He does add aft wings under the water to give it a reasonable planing performance though.

In other words, it's possible to make good boats for particular purposes from designs that are not nearly as good for general use as most novices think. So, I agree with your attempt to make messman think seriously about the problems of the dory before jumping into a building program.

messman

11-22-2008, 05:13 PM

I am very open ideas here, and I am not stuck to one design. I do like the design concept of the Cat. and want further options. The Dory design that was presented by rasorinc is very similar to the Dory design I am looking at from Spira, the one problem is that with it's 9' 8" beam it's not trailable, major draw back there. Here is the dory design I am concidering, which is based on the Pasific dory designs. http://www.spirainternational.com/study/SitkaStudy.pdf
It seems to have the wider bottom that Tom has pointed out in his post. I guess I should have provided the link with the initial posting, sorry.

Please more discussion on this issue, I truly want the input from you all. This will allow me to make an informed decision rather that jumping into the deep end of the pool only to find that it was filled with jagged rocks.

Chris

rasorinc

11-22-2008, 05:18 PM

here is a trailable dory and cat. How many people will you have in the boat? If you want to do motor sports the Dory is not the boat to do it in. The Cat gives you much greater flexibity in usage. Stan

https://www.boatdesigns.com/products.asp?dept=900https:

https://www.boatdesigns.com/products.asp?dept=372
If you go to the Glen L site, go to customer photos you click on Wildcat and you will see a complete building job. Click on V dory and you will see various builds. Just more info for you. Hope it helps

messman

11-22-2008, 05:35 PM

Thanks Rasorinc, I will take a look at these.

Chris

tom28571

11-23-2008, 01:42 PM

I thought I would throw in some numbers that may help see the difference in different "dory type" boats and lead to better understanding of the types. If the crew stays inside the beam of the hull bottom, most any boat can be considered stable. In a very narrow bottom dory like Bolger's Light Dory, you need to sit in the center with your hair parted in the middle.

A good indicator of tenderness is probably the hull bottom beam to sheer beam ratio. Some numbers for a few boats are:

Bolger Light Dory ~ 0.5
Glen L Big Hunk = 0.62
Gerr Offshore Skiff = 0.62
Spira Pacific Dory = 0.67
C Dory = 0.71
Simmons Skiff (typ) = 0.71
Tolman std = 0.71
wide body = 0.73
Jumbo = 0.75

Typical non dory ~ 0.80
Bolger box = 1.0

Moving from top to bottom on this list gets you from very low to very high initial stability. It does not show that any of these boats are safer in all conditions than any others so one with even very low initial stability may stiffen up more or less than others when heeled. Comfort, especially in cruising, is often closely dependent on initial stability though. A fishing boat can, in my view, accept much lower initial stability than a cruising boat, especially as there will always be some high up structure that makes stability worse than the number might indicate.

I would think that the Simmons and Tolman Standard are fine for a fishing boat but barely marginal for cruising. I'd place the C Dory a bit low on that scale while realizing that there are scads of owners ready to skewer me for that opinion. I and some of them, if they admit it, have had a C Dory become very stable on its steeply flared side after a roll going downwind. Not what I call comfortable.

I'd like at least 0.75 of the Tolman Jumbo and preferably nearer to 0.80 in the range of Devlin's small cruisers. Bolgers boxes rate so high here because their sides are vertical and it is not possible for the crew to be outside the bottom beam. I would have no qualms about going offshore in Gerr's 28' Offshore Skiff but would not care to take a cruise in one. Stepping aboard one at the dock is a surprise and you should warn anyone aboard when you do that. It banks waaay over in a turn and I expect other small boats with a similar ratio to do likewise. The one I drove was owned by an airplane pilot so he probably did not mind too much.

These are my personal thoughts and I would like Tad's or others views here.

messman

11-23-2008, 02:06 PM

Tom,

That is verying interesting information. How do you come up with the number, or in other words what formula do you use to come up with the number.

Chris

ancient kayaker

11-23-2008, 05:48 PM

You can have too much of a good thing when it comes to primary stability, especially if you are caught between wind and water and a crew member has a sensitive stomach. It's the secondary stability that actually saves your butt in a blow.

PAR

11-23-2008, 06:46 PM

What Tom wisely points out is that one; there are many different types of dories, two the type has evolved considerably, incorporating many variants all called (many not rightly so) dory and lastly, that modern renditions of the dory are considerably different then the real dories that were fished extensively in the 19th century.

The 19th century dories, for the most part (all 15 or so variants) were heavily built by modern standards, though considered light in their day. They were also intended to "load down" uniformly, without ill handling or bad manners while bringing home a ton or so of fresh fish. These types, when lightly loaded are considered quite tender by today's standards, though an acceptable trade off then. These "antique" craft, should be left to those interested in preserving the type, because as sailors or pulling craft, they suck frankly.

Enter the modern dory or what is often referred to a semi-dory or modified dory. These are more skiff like in appearance, having less flare in the topsides, less height in the aft portions of sheer and most importantly a wider bottom beam to improve initial stability. Other features will include considerably wider transoms, compared to the tombstones typical of the antiques or the fat buttocked double enders. These "improvements" are a natural progression of the type and for the most part have changed them into a different breed.

If a modern semi dory (power version) or modified dory (sail) hull form is selected, for a designer familiar with the type, then you'll do well with your planned excursion/dive boat. If you elect to "doctor" up a conventional dory or a hull form that isn't well suited to your intentions, you may well end up with a boat that you just don't like to be out on.

Personally, I wouldn't select a dory for a dive platform. For this you want a boat capable of moderate deep water work, but a reasonably stable hull form. A dory, modified or not, isn't well suited for this. Weight needs to be kept very low in a dory, so out goes the cabin idea.

If working in the coastal gulf and other Florida waters, you'll want shoal draft, to go along with this stable platform. This means a much wider beam/length ratio then typically found in dories of any type. I'd recommend a Sea Sled design for ultimate stability, extreme shoal draft and lots of deck space for a house. If this shape frightens you, then a moderate V hull, with 16 degrees or less of deadrise. This will handle the occasional trips off shore, while still providing stability.

There are a lot of questions yet decided about your needs, much of which will help determine the hull form you need, such as the desired general speed, power train, percentage of time parked over a diver, compared to exploring the coastline, accommodations, equipment, budget, etc.

tom28571

11-23-2008, 07:20 PM

Paul,

That adds a lot of flesh to what I was saying. I hesitate to say too much about the dory as a type, because there have been so many changes and some people have a fixation on them. In general, I think there are better boats for almost any use than dories which have been modified in an attempt to meet such requirements. Any use needing work to be done over the side, like diving for instance, will suffer from very much flare, which is the main feature of a dory.

Messman,

It's not much of a formula, just a measure of the flare of the hull sides. Just divide the max hull bottom beam by the max sheer beam. Higher numbers represent higher initial stability and vice versa. Smaller boats are more affected by the result because loads like crew weight, gear placement and any superstructure like a cabin have relatively more effect on stability in small boats than in large ones. Larger dories are also more likely to have some ballast.

ancient kayaker

11-24-2008, 12:56 AM

The usefulness of the true dory is long past, it's kept alive by enthusiasts with a historical, not a practical perspective. In its day its advantage was it could be built cheaply by nearly unskilled labor and, if you got a few important dimensions right, it would work as expected, even if your workmanship was a bit off. Also, if you got caught out in a bad blow far from shore or the mothership you can lie down in the bottom of your dory with a good chance of corking it out alive, and a dory can haul a heck of a load. Dories carried on a ship for fishing etc were made with removeable thwarts and seats so they could be stacked on deck.

I based my first two boats on the dory concept for its simplicity and ease of design. Pretty to look at, but awful things to use; suffice it to say, my designs have moved on.

I think there are better places to start for almost any boat unless your requirements correspond with the needs of its inventors. Now I have to head down to the bomb shelter ...

PAR

11-24-2008, 01:12 PM

As I mentioned, the dory, as we now know it, really is a new type unto itself, vastly different from the "antique" craft of which so much has been written. I have to admit to a bit of historical interest so I'm happy to pass along some of the evolution, which most (exceptions noted) aren't aware.

The dory has a very interesting evolution. It's an area specific type, so much so that as the model moved from one area of the country to another, it had to be modified to suit the new conditions. It developed quite differently in different parts of the USA as a result, each being better dressed for it's local environment.

I built a 27' St. Pierre about 30 years ago. I sailed it for a few seasons and then converted it to power fishing operation. I sold the boat only a few years after building, because it sailed poorly and as a fishing boat, lacked a lot of things. It was a reasonably accurate representation of the modified dory seen today, with a wider bottom then the antiques, but not as wide as currently is fashionable, wider stern and less flare. If I was to do one again, it would retain the narrow bottom of the originals, a little less rocker, a little more beam carried aft and considerably less flare. This would make a much less volumes hull, but one that would drive easier when pressed.

If I were in Chris's place, I'd be looking at a flat bottomed skiff as the most economical way to get on the water, with his desires, but possibly not the best suited for his wishes. The V bottom of moderate deadrise would be a better choice, but at slightly more building difficulty.

For a cabin boat, you need hull depth, which is difficult if the boat is to work Florida's waters. Getting hull depth in a flat bottom is difficult and much easier with a V bottom. The benefits of course are the cabin doesn't look like a Winnebago isn't parked on the foredeck and you can keep the CG in a reasonable location.

Cats are an option as are other hull types like the Sea Sled.

messman

11-24-2008, 11:50 PM

I am loving this discussion all, just thought I would let you know that. Ok back to subject.
Ok, so what I am hearing here is that a dory, even the one I am looking at probably would not be the best choice. For the following reasons:

1. hull design is not the best for all intended purposes, ie hard to get in and out of for swimming or diving.

2. It basically handles like a rat (dead) in a trap

3. probably would not do well with a cabin (even the more modern types)

Now the question is what should I go with. The Cat, Sea sled, and a V bottom design have been suggested so far. Here is what I want to use the boat for (In order of preference).

1. Family outings
2. Fishing
3. Swimming/diving platform

These activities shall be done with over night outings, none currently planned for longer than 3 nights. Time does not allow for longer ventures.

My woodworking abilities should be able to handle most of the challanges that will come along with what ever design I finally go with. But I would really like one that will be fairly easy to build, I want to enjoy building it, but I would rather be able to enjoy using it, if you know what I mean.

So what would you suggest and if you feel inclined to explain, why do you suggest it?

Thanks everyone. I am really enjoying this and I am actually learning alot.

Chris

Boatpride

11-25-2008, 02:35 AM

Hi Chris

your welcome! Yes he does seem to have a business incentive, but his niche is a strong one.

Best of luck and let us know!

tom28571

11-25-2008, 10:01 AM

Chris,

It you assume that the guys who buy, build and use boats for these purposes have some insights to the better boat for the job, then the order would be like this. Monohull V, cat, and sled, with the sled being almost non existent. Some will say that the sled or inverted V (IVB) is the best boat though. So, it boils down to you making the decision anyway.

If a cat is to have much room inside, the connecting bridge must be high enough off the water that chop does not strike it. I recently took a 45 mile trip in inside coastal water in a 36 foot power cat that was miserable because the designers/builders had sacrificed underway comfort for dock comfort. Chop would hit the underside and make the whole boat shudder. The return trip was fine in calm water. If the underside is high enough that chop does not hit it, a small trailerable cat gets pretty top heavy and prone to capsize even though the initial stability is very high. The designer has to cut a fine line between these competing objectives.

The sled is probably similar to the cat but I don't have any experience with them. Very few people do have experience with sleds and many of them may have vested interests, so caution is advised.

Within the monohull platform, there are many different types, flat bottom, deep V, shallow V, lobsterboat, the dory, etc. In general, I think the monohull has more to offer for a broad spectrum of uses than the others but that is my opinion, for what its worth. A self draining cockpit is high on my list and for diving, a gate in the transom to a platform would be great.

PAR

11-25-2008, 11:09 AM

I have experience with sleds and they are easily the best rough water, shoal draft boat going. One ride in a nasty chop and you quickly see it's advantages. Unlike a cat, it gathers it's bow wave up and stuffs it under the boat. The resulting lift and air do several things one of which is swallow up chop like it's not even there. The other nice thing is it's efficiency, which is quite high, especially compared to deep V monos or well burdened cats. This is because the interface between boat and water doesn't cast a high percentage of water aside, but employs it to cushion the ride and generate dramatically more lift. This means more speed from the same HP on other, similarly sized and equipped hull forms.

My first experiences with a sled was on a real Hickman racer. It was an eye opening experience. Next was a modified sled, which had wider chine flats and built lighter. It literally hops up on plane with no transition, just a smooth rush.

Honestly there are many designs, in all the hull form categories, that could suit these needs.

Chris, the design selection process can be a difficult one. There are so many things to balance and counter balance during your considerations. Building ease, in both the design type and construction method, material choices, hull type and accommodation requirements, a target performance envelope, the list is pretty involved.

As Tom has pointed out, the decision is ultimately yours. You are the best skilled person to access the merits of specific designs. Try to find designs that incorporate as many of the features and desired qualities as you can. From this assembly, you can make a "pro and con" list to see how each stack up.

tom28571

11-25-2008, 12:55 PM

Paul,

One thing negative about sleds that I have heard, from Bolger, I think. He said that that in rough water the sled can slam down and puff a wall of spray back out the bow and over the cockpit, creating a new form of misery. Have you had this experience? If so, how bad was it.

We had one forumite who extolled the virtues of the IVB. Trouble was, his message was so messianic that he was mostly ignored. It's an interesting concept though.

messman

11-25-2008, 08:49 PM

PAR and Tom,

And everyone else who has participated in my education here, again I thank you. I do understand that I have to make the final choice. I asked the question because my knowledge is limited and I want to make the most informed decision I can. I have been reading what I can, when I can to help get over the learning curve. The information that is being given to me by you all is being very helpful, even though I have more questions now than ever before. But these are questions that I know I need to answer prior to saying yes this is the boat I am going to build. And many of the questions I know I have are questions that never even crossed my mind, thank you so much for that.

I very much welcome everyones opinions and experiences, as these only allow me to see things I need to think of prior to committing to a design. As I see it I want to choose a design that is stable overall in most all conditions. Speed is not an issue for me, I am not going to firewall my boat unless there is some sort of emergecy that requires it. But I do want a vessel that is going to sip fuel at it's cruizing speed. (everyone is probably saying he wants it all and he can't have it all) :D What can I say call me crazy :P I know that something has to give somewhere.

There was a boat featured in a 1973 issue of Mechanix Illustrated I called the Budget House Boat (attached file). I liked the concept of the boat but have shided away from it because it would appear to be for only calm waters such as lakes. Do you believe I am correct in this assessment?

Again Thanks all
Chris

PAR

11-26-2008, 01:09 AM

Yes, Tom the old Hickman style designs were prone to this. They also had other bad habits, but you must remember the originals were racers designed many decade ago. Some of the other issues are the anti trip chines on the Hickman style, tended to still permit the boat to trip in high speed turns, they attempted to use a "sneeze guard" to stop the blow back in rough going. These worked to a degree, but there are better ways around it.

Bill Jackson and a few others starting in the 50's when the military's interest was re-kindled, started to refine the design, but it still fell short on some points.

Newer designs, like mine and others, have addressed all the issues. The sneeze issue was a function of the quick bow turn and entry angle in profile. With more rake this problem disappears. A re-shaped chine and centerline, removal of the reverse deadrise at the transom, introduction of topside flare plus considerably wider and steeper chine flats solved the other issues. With a jack plate you can run in just inches of water with these things. They are gaining popularity all along the gulf coasts.

The PM Budget House Boat is really a house boat, though capable of motoring around protected waterways (lakes and rivers). For your needs it's very unsuited, as it would beat you to death waiting on a diver in moderately deep water. Picture a large concrete mixing tub with a small shack on top of it and this is pretty much what this boat is all about.

http://www.bateau.com/studyplans/HB20_study.htm?prod=HB20 this is a much better version of this style of boat. Again, you wouldn't want to venture into deep water with this.

http://www.bateau.com/studyplans/P19_study.htm?prod=P19 this is a better choice for your needs.

Loveofsea

11-26-2008, 04:25 AM

tom28571

11-26-2008, 08:39 AM

Paul,

Liz and I are off to the beach for family turkey day but I would like to look at your innovations to the sled when I get back. Some of them I have heard of. I thought Hunt's cathedral hull (Boston Whaler) grew out of the sled and avoiding Hickman's temper and patents.

I've corresponded with Brad and seen photos of his boat. He goes after the rough riding habits of flat bottoms in a similar way to that which I use on some V hulls and successfully runs them in the ocean. I'll let him write on just how he does it.

Happy Thanksgiving everybody,

Gotta run.

CET

11-26-2008, 03:29 PM

I designed and built a 19ft flatbottom dory back in '91, since then i have logged over 60,000nm of open seas here in Southern California. Forgive me for making such a brazen ststement, but i have never seen a commercially available design that gets it right. If designed correctly, the dory is an extraordinarilly safe and sea worthy hull configuration. I couldn't run the seas they way i do in any other hull type. I am pressed for time at this moment, but i would be happy to share some of my design innovations with you.

Brad

(loves the sea)

Brad, I too would be very interested in your design modifications and innovations for the flat-bottom dory. I am actually in the process of playing with some dory designs right now for use as an inshore fishing platform for So. Cal. waters. Would love to hear what you have to share and see some photos, if possible.

Happy Holidays!

messman

11-26-2008, 06:46 PM

I would love to hear and see what you have done as well.

Chris

messman

11-28-2008, 11:45 PM

Brad,

I would love to hear and see what you have done.

Chris

Loveofsea

11-29-2008, 01:42 PM

Here are a few things that make this hull work so well. The hull is flat all the way to the bow. The widest part of the hull is 2/3 forward, and 8" wider than the transom. i carry 54 gallons of fuel in the fwd 1/3 of the hull (in portable tanks that nest under the deck) I use a SST lifting strake across the transom with a cutout for the engine to create exagerated transom lift..

__in other words, most of the weigh is pushed max forward. The impact point of the hull is 2/3 fwd where the hull is the widest..

two opposing factors come into play here--the inherent bow lift from pushing a wider fwd hull over the water and the exagerated trasom lift from the SST lifting strake across the transom. The hull creates lift both fore and aft---that has the effecy of keeping the hull stuck to the surface. if it doesn't lift, it will not slap back down. The impact point (the widest point) uses the extra weight of the fuel along with the exagerated transom lift to crush the water and send it out the sides.

Here is a link to a stroy that was done about the 'Good Skiff' last year...

http://www.oceanskiffjournal.com/

TeddyDiver

11-29-2008, 03:04 PM

So what would you suggest and if you feel inclined to explain, why do you suggest it?
I know quite well what you are talking about. I started a project with quite similar preferences.

Some exceptions:
1. Longer cruises. Up to some weeks
2. Not only for family but also for ugly gents talking dirty:D

I was unable to find any designs for diving and fishing meeting my demands so here's some sketches what I'm currently building (there's some pictures of the hull under construction etc) but you get a general idea what I'm doing, and maybe it will give you some thoughts and help you to find design for you
http://www.boatdesign.net/gallery/showphoto.php/photo/9948/ppuser/23741
BR Teddy

CET

11-29-2008, 03:17 PM