Round stern vs box stern??

[Deadrise13]

Would a round stern boat (like a cheseapeak bay deadrise) be Faster than a more traditional box stern?? Is there a differance in drag, Or dose it make a differance?? Thanks

[robherc]

Hmmm.... Chesapeak Bay Deadrise..from the photos on Wikipedia, has a box-stern....I'm confused :confused:
...what exactly are you looking at? can you draw us a picture?

[Deadrise13]

Thanks for the reply. Check out----- The Albatross fleet of Hatteras NC. ----Sorry I am new here and do not know how to post a picture yet. They have 3 old deadrise boats all of them are round stern. I grew up fishing on them as a kid with my pop. Thanks again for the input.

[apex1]

Thanks for the reply. Check out----- The Albatross fleet of Hatteras NC. ----Sorry I am new here and do not know how to post a picture yet. They have 3 old deadrise boats all of them are round stern. I grew up fishing on them as a kid with my pop. Thanks again for the input.

Go to your post... click edit...go down to the button "go advanced"....
go down to the button "attachments" or "manage attachments"
upload.... smile!:D
Regards
Richard

[robherc]

OK, that's what I was thinking you were asking, but I wanted to make sure you meant round-stern & not round-bilge ;)

Anywise, the rounded stern will give slightly better efficiency at lower speeds (below planing). The rounding of the stern allows the water to close more smoothly behind the boat, but will actually increase drag on a boat that CAN plane. Since those boats are listed as being 45' boats (hull speed = 8.72kts) & they're showing 18kts cruising speeds on them, I'm wondering why they would have made the trade-off there?
Maybe I'm missing something though...if you wait a couple hours, I'm sure someone else will point out my error. :P

[Deadrise13]

Thanks to both replys, I should be able to post pix next time. And that is what the old guy that is going to build my new boat said. He thought round may be a little slower. I will see what some of the other guys say. I am trying to get the best speed for the $. I do like the look of that round stern though. Thanks for your time. I knew I could find lots of help here!!

[Roger Moren]

You can have both. Tampered stern at the waterline ( min.stern wave ) and flairing to actually having a stern, providing lift.

[Deadrise13]

So you are saying it is a wash?? If so I would go for the look!!---Thanks---

[PAR]

Are you talking about an elliptical stern? If so the elliptical stern will have little, if anything to do with performance, unless it's immersed, which it most often isn't.

[Deadrise13]

Thanks for all the input, it seems it dose not make that much differance either way. The boats usally are under 25 kts top speed. Just trying to milk every bit of performance I can.

[Leo Lazauskas]

Thanks for all the input, it seems it dose not make that much differance either way.

I wouldn't be too quick to leap to that conclusion. None of the replies mentioned any calculations, nor did they point to any experiments supporting their guesses.

[Leo Lazauskas]

You can have both. Tampered stern at the waterline ( min.stern wave ) and flairing to actually having a stern, providing lift.

You are guessing. No stern wave can also mean that there is nothing to cancel the bow wave, and therefore wave resistance will be greater.

[robherc]

Deadrise:

There HAS to be some difference made by it, or nobody would make them. The question is: what was their reason for using it?

The most likely possible reasons I can think of off-had are:
Low speed efficiency;
Aesthetics;
Extra deck space.

That doesn't mean that there isn't another reason that I'm missing, or that any of those reasons are necessarily practical/plausible...they're just guesses. Your best resource may be to find someone who designs boats with those stern shapes & ask him why he did it. ;)

[robherc]

You are guessing. No stern wave can also mean that there is nothing to cancel the bow wave, and therefore wave resistance will be greater.
I think it's a safe bet that every poster in this thread is guessing.

[Leo Lazauskas]

The rounding of the stern allows the water to close more smoothly behind the boat, but will actually increase drag on a boat that CAN plane.

Do you have any support for this guess.
The air cavity behind a transom is vented to atmospheric pressure, and so it cannot sustain a pressure. So how does the shape of this cavity increase or decrease (for example) the wave-making component of resistance?

[robherc]

Mostly guessing...at slow enough speeds I see having similar gains by a rounded stern to what is gained by a double-ender (though the DE would get higher efficiency, and at higher speeds). At planing speeds, I see the rounded bow as increasing the overall wetted area aft with very little added lift, thus loss of efficiency & more of an "X" shaped stern wave until a high enough speed is reached to completely disconnect the flow from the curved sides of the stern (which would be above the stated 25kts max speed).

While I will not work up fluid-dynamc/hydrodynamic formulas to post here to prove my assumptions, if you depart from your calculator for a minute & try to look at things from the viewpoint of logic & physics intuition, you'll see what I mean very quickly. ;)
Yes, I CAN do calculus in my head, but I very quickly learned the worth of "throwing away the calculator," so to speak, for some things after High School. :P

[robherc]

Oh yeah...almost forgot:
All of the above information is based on the assumption that the rounded portion(s) of the stern ARE wetted.
Also, by rounding the stern, you're adding a couple feet to the LWL...thus raising hull speed, but I still don't see where that's a benefit for a planing-speed craft.

[Leo Lazauskas]

Mostly guessing...at slow enough speeds I see having similar gains by a rounded stern to what is gained by a double-ender (though the DE would get higher efficiency, and at higher speeds). At planing speeds, I see the rounded bow as increasing the overall wetted area aft with very little added lift, thus loss of efficiency & more of an "X" shaped stern wave until a high enough speed is reached to completely disconnect the flow from the curved sides of the stern (which would be above the stated 25kts max speed).

While I will not work up fluid-dynamc/hydrodynamic formulas to post here to prove my assumptions, if you depart from your calculator for a minute & try to look at things from the viewpoint of logic & physics intuition, you'll see what I mean very quickly. ;)
Yes, I CAN do calculus in my head, but I very quickly learned the worth of "throwing away the calculator," so to speak, for some things after High School. :P

Sorry, but I can't accept your faith-based assertions. :p

And as for "I have seen similar gains...", where is the data to support this? It would have some credibility if you could supply real figures, but at the moment it is little more than hand-waving.

[Deadrise13]

From what I have read they started using round sterns on work boats for one reason. When thay would pull there big gill nets in the rear deck of the boat they would not get cought on the back corners of the boat.

[robherc]

Deadrise:
OK, then is was guess #4: Something work/fishing related :P

Leo:
If you meant "I see having similar gains..." then it's self explanatory...don't mis-quote me and you won't confuse yourself.
I have already explained my position perfectly, and have at no point asked anyone to accept my theorems as fact. That is where you went wrong, you're wanting fact & mathematical support for everything that I've already directly stated I wasn't going to give you. And if you re-read my post #14 I think it's a safe bet that every poster in this thread is guessing.
I don't think I can put it any more clearly than that. If you don't want to hear theories based on sound logic, but NOT on math, then simply ignore most of my postings, and I'll not be too offended. There are plenty of us in here that can accept something on a logical level without needing a mathematical equation to explain it to us...if you need the equation, run it for yourself, or ignore posts from anyone who doesn't offer their equation up-front.

[Leo Lazauskas]

Deadrise:
If you don't want to hear theories based on sound logic, but NOT on math, then simply ignore most of my postings, and I'll not be too offended.

But it's not sound logic. It's gibberish. :p

[Deadrise13]

Her is the boat I am asking about

[DMacPherson]

I am loathe to step into the fray here, but the tone has taken a turn and I'm compelled to reply. I think you are missing Leo's very reasonable statement - that the assertions are anecdotal, at best, without the benefit of test data. I don't read any of his posts that says he wants the equations or formula, just some real in-the-water performance results to compare. That's just good engineering, and has nothing to do with crunching any numbers.

Regards,

Don MacPherson
HydroComp

[Deadrise13]

More pix of the Albatross III of the Foster fleet Hatteras NC. Thanks for all the replys

[robherc]

@Leo
I think you need to re-research your basic physics & hydrodynamics buddy...I've shown you no disrespect, but you're being spiteful (not to mention WRONG)...please do try to clean it up a bit...you're quickly backing yourself into an indefensible position here.

[robherc]

@Don,
Sorry, but I don't have $10,000's to invest in test results on every idea that is expressed in this forum. I am a hobbyist, not an engineer with a company/college and unlimited testing resources at my disposal. Deadrise asked for opinions, and I gave mine....so far yourself & Leo are the only ones who can't seem to accept that.

[Deadrise13]

Thanks for all the thoughts guys, I guess if it has worked all these years for the Albatross fleet it must do ok. They have fished these same three boats since the therties.

[robherc]

Do you have any support for this guess.
The air cavity behind a transom is vented to atmospheric pressure, and so it cannot sustain a pressure. ...
I present exhibit #1...there is no "air cavity" in the (wetted) rounded-stern I was illustrating, therefore THIS post (by Leo) is the one that's filled with "jibberish." ...cut by your own knife...

Anywise, this arguing is becoming pointless now, as Deadrise posted another picture, and the new, profile-view, picture clearly shows that the rounded-portion of the stern is NOT wetted.

[Deadrise13]

Sorry for all the pix I am just happy to know how to upload. When you guys figure out what the right answer is could some one tell me in plain english. Thanks for all the input.----

[Leo Lazauskas]

@Leo
I think you need to re-research your basic physics & hydrodynamics buddy...I've shown you no disrespect, but you're being spiteful (not to mention WRONG)...please do try to clean it up a bit...you're quickly backing yourself into an indefensible position here.

Physics and engineering are about measurement and calculation. You were trying to promote a brand of snake-oil and I called you on it. :P

[robherc]

Keep to the facts, I promoted nothing but an opinion, and called it as much when I gave it...you're the one mis-quoting, and trying to read more into my posts than I put there. Stick with the facts, or stick your nose back out...you have yet to add ANYTHING of substance to this thread. All you have posted AT ALL here is to attack other people's opinions without either proving them wrong, or giving your own...welcome to the "blocked list".

[PAR]

My post wasn't speculation, nor any guess work as has been indignantly suggested. I'm very familiar with the stern shapes used above, it's one of my favorites, one I've employed it in several of my designs and as I posted earlier, will impart no difference on the performance of the vessel. Shown are elliptical stern vessels, typical of the type I used growing up in they very area they are from. They clear the LWL and at best will kiss it when squatting under way, which will not affect the performance envelope in any noticeable regard. If you bother to test, the sterns that are slightly immersed will show a very slight increase in drag, but not enough to get concerned about as we're talking a fraction of a knot.

The reason for their use, which was finally mentioned, was to prevent fouling the gear and nets as it was dragged back aboard over the stern. It also was a way to gain additional working deck space well aft, while having relatively balanced ends below the LWL. This was typical of the displacement craft from which the type was derived. As power was introduced to these types, the sterns took on a different, considerably fuller shape below the LWL, but retained the elliptical stern for practical reasons.

The first photo posted by Deadrise13, clearly shows the transom is clear. The second and third images show the semi plane version of this type, where the stern is just kissing the LWL, but provides a fair amount of bearing area when she squats. The fourth photo is clear enough, but appears also to be a semi plane hull. The other photos don't show enough to offer much information, but much can be gathered from the 5th image as they all are in semi plane mode.

In plain english, it's a lovely stern, particularly if kept clear of the LWL. If used on a planning hull there often is a distinct knuckle used to provide bearing area aft as she squats. If a displacement mode boat, then it's kept clear. It offers stylish and effective deck space aft on a fine ended craft, isn't as effected by following seas and breaking waves as a traditional transom is and isn't as hard to build as you might think.

For those that would rather find fault or offer less then productive replies, then maybe they should just go back to the pub and suck down a few more beers instead.

[Leo Lazauskas]

For those that would rather find fault or offer less then productive replies, then maybe they should just go back to the pub and suck down a few more beers instead.

What's wrong with finding fault, or asking posters to substantiate their unscientific guesses and loopy speculations?

[Deadrise13]

Hey Par, it seems you have a special spot in your hart like I do for a dieing haratige. As I said I grew up on the bay and have a very special part of my past spent on these type of boats. Now I live in Fla the land of the supper boats, Don't get me wrong I love them as well. I am having a boat built this summer like the Albatrose and really appritiate all the help. I am trying to figure out how to power it. I want some sort of econamy, but need a little speed on the runs. My off shore run is about 25 mile each way and I am going to fish this boat hard. Once again thank you for your help, It shows you know your stuff and have a working knowledge of a peice of Good old American haritedge. Any Ideas on the power plan, type eng, size, set up. The boat will be 45' x14.5'. Funny when I ask the Old gentelman that is going to build her how much she will way, He said in a Harkers Island voice "I don't Know I anit never weighed one". Fine with me, they have done the job all these years, I think it will turn out just fine. I am jellouse of the guys that can figure this stuff out on a caculatore. Thanks again for all the positive input!! Peace--------

[PAR]

Without a more defined design brief, I wouldn't want to speculate on propulsion hull form, etc.

I suspect the old timer will build what he wants to build regardless of what the plans provided. This is more often the case then most realize, as the average owner couldn't tell the difference between 14 or 17 degrees in deadrise, if the builder "thought it should be this way". Most of the time they produce a boat that is inferior to the drawn plans, but it's difficult to compare so, they get away with it.

I've designed quite a few elliptical stern craft and have specialized in shoal draft as in the Chesapeake and here in Florida, it's always been an issue with me. Who's doing the design work?

You mentioned 25 knots as the top speed of the boats you're familiar with. Assuming they're around 40' LWL, at 25 knots they're pretty much up on full plane (2.9 S/L). Semi plane speeds (what most are capable of) would be from about 9 knots to near 20. Displacement would be below 8.5 knots of course.

The displacement hulls will be the most efficient in fuel savings, with increasing speed, exponentially increasing fuel costs and HP requirements. This could be mitigated to some degree with a narrow beam/length ratio, but most working craft want the beam and just pay the price.

[ancient kayaker]

Lovely yes, and great for fishermen, but those round/ellictical sterns must be much more difficult to construct. Just in case you're thinking of getting serious.

[PAR]

No they’re not as bad as you’d think Terry. The traditional way was vertical staves, which can be tedious, but not so tough. On my plywood designs, I use a conical section, which permits a piece of plywood to wrap right around with no trouble. On a planked hull, the planks take on some pretty weird shapes, but it can be done.

[Deadrise13]

PAR, Thanks again for the input. I do understand your reservations on advice without facts. I will come back at a later date with more info as I get it. This prosses will take a year or more and there should be plenty of down time to look into the details. To the round stern construction process, I would not take it on myself but the gentelman that is going to build the boat has been doing it for 55 years. He is a native to Harkers island NC and we all know what has come from that readgen of the country in reafrence to uniqe desine. Caralina Flair, I would pick to top off the list. Forgive me I have only scrached the surface in my reaserch, but should know quite a bit more about there boat buildeing culture buy the end of this build. When I ask him how hard it would be to go round vs box he just laghed and said "It aint that bad, just takes a little longer". Thanks again for the continued input------

[PAR]

Send me his name and where he works in an email, it's likely that I know him and can provide the "low down".

[BMcF]

What's wrong with finding fault, or asking posters to substantiate their unscientific guesses and loopy speculations?

Oh Leo..[sigh] there you go wanting the science to work again. :D

This thread has been a hoot, simply because I live right where so many of those specific boats were invented, built..and rebuilt..and modified. I still drink a beer every now and then with Francis Goddard, Ben Goddard, Billy Deagle, Donald Thompson and a few others..the few who remain that banged out those things (and bateaus, skipjacks, buy boats, and various working skiffs) one after another. Not a one of them could probably even use a calculator..but all built beatifull vessels.

Nearly all of the 'original' wooden roundsterns hereabouts (as differentiated from the box-sterns and drake-tails) have had what are called locally 'settling boards' added to them so they could benefit from the advent of V-8 engines that made a whopping 100HP (or more). 'Settling boards', quite simply, are big flat planks attached to the bottom of the hull and extending aft, supported by reach rods that are attached to the rising portion of the roundstern near or above the orignal displacement waterline.

Thus is achieved speeds well above the orignal design, with the higher installed power of todays engines, of course. ... next time my pal Greg pulls his 1940s vintage roundstern with setttling boards out for annual paint, I'll try to snap some pics.

St. Georges Island, MD

[Deadrise13]

Hey BMcF, I think I have a pix I can scan of that plaining board. I will try to post it. THANKS FOR YOUR INPUT-----

[Deadrise13]

PAR, I did send you an e-mail. Let me know if you did not get it!?!? Thanks

[Deadrise13]

I think this is the plaining board BMcF was refering too. Sorry for the bad pix it is scaned out of the waterman of the cheasapeak bay book.

[BMcF]

I think this is the plaining board BMcF was refering too. Sorry for the bad pix it is scaned out of the waterman of the cheasapeak bay book.

Yes..quite the typical retrofit detail as seen from above the water. A crude but effective means of making a displacemnt hull at least a semi-planing hull....

I've yet to see one of the roundsterns with the settling boards added reach the speeds the typical box-stern deadrise dories do with the same power though. That is just a personal observation of those here locally....

[PAR]

Even with the bilge runners (settling boards), the displacement hull runs are usually too steep to permit much more then 2.5 S/L. They do help considerably at 1.5 to 2.5 S/L though, which is semi plane mode. A full plane hull can be developed with that stern shape.

Greg, I did get your email and yep, I know him. I'll send you what I have in a few days. I got to go sit at a booth in a boat show, which I just don't like to do, but was talked into it.

[liki]

Here you can see a bit more sophisticated retrofit:
http://www.friddemartin.net/fanny/picgallfi.html
:)

The texts seemed to be only in Finnish but a traditional wooden displacement hull was turned into a +40kn performing monster powered with 440hp yanmar and a 2-speed marine gear.

I've heard rumors that the engine already into one with well over 500hp.

[BMcF]

I got to go sit at a booth in a boat show, which I just don't like to do, but was talked into it.

Miami Brookerage Show I'm guessing?..missed that this year but have some associates hanging arounf there...

[Deadrise13]

Got it PAR, Thanks I will look forward to hearing from you.-----Nice pix Liki----Thanks for the input, I will check them out tonight.-----

[kmorin]

Deadrise13,
I'm not a wood boat man so I haven't a clue about building these hull forms in wood, but I do have a few notes to add here about his particular stern's behavior at sea.

Almost without regard to exact type- net fishermen face a gear related displacement event when they have lots of fish. Even drift gill nets get a large concentration of fish in one location, needless to say trawls, draggers and seiners all concentrate their catch too. So net fishermen often have to load their catch in a large bunch instead many single wts added over time like the hook and line or long liners.

If you're working the net over the stern and have to add lots of wt to the hull in a short time then a following sea can board more easily if the hull shape has less reserve buoyancy like a squared off, plumb transom. A rounded shape or conic form increases the RATE of increasing buoyancy as its settled deeper in the water.

Many traditional commerical fishing net fishermen found the fan tail, conic, or rounded and flammed stern to be drier and safer when working their gear. This is one reason for the shape in older working boats.

In a following sea, especially with a loaded fishhold, these shapes are much more steady on course. The transom stern power boats require a good deal more helm, more often as the waterlines aft are less rounded and therefore more vector is imparted to the hull's movement by overtaking seas.

Rounded, fan tailed, or conic stern forms generally have a less angular vector to yaw the helm about the keel, as the form provides a more uniform lift and less 'one side or the other' thrust by the oncoming (following) sea. When loaded a fishing boat's helm can be a bit of a chore, the crew is often tired and the run might be at night, so contributing to the success of these shapes was also the conditions in which they were most used.

I use these forms in metal boats because I like their looks, they are less tiring to fish in the open ocean, and with a simply angled step plate you can transition from square stern line of planing shapes to the nicely rounded stern.

And who among us doesn't enjoy a nicely rounded stern?

cheers,
Kevin Morin

[Deadrise13]

I for one Love a nicely Rounded, Firm Stern!!! Ow you ment the boat, forgive me. Thanks for all the input. I will not be comercially fishing this boat. I will be hook and line fishing off shore. I Have heard much of what you are saying from some old fishing buddys who did it all back in the day. I would probabaly think long and hard if I was going to use the boat for other reasons. Could you explain the angeled step plate idea? I think I know what you mean but would like to be sure! Thanks for all the input----

[kmorin]

Deadrise13,

I only build in metal so I'm only discussing metal in this reply. I don't know about wood construction well enough to predict if there's any way to do this reliably in wood.

http://i383.photobucket.com/albums/oo273/kevinmorin_photo/Titan%20Tug/Tugsternwaterline_1a.jpg


First is an image of a little round stern tug shape without the keel to keep the image simple. The sketch shows her from a few views confirming the more or less rounded stern but because of her rising butt lines the water line is rounded too. Many designers want a more squared off after surface for planing hulls.

http://i383.photobucket.com/albums/oo273/kevinmorin_photo/Titan%20Tug/Tugsternwaterline_2a.jpg

This just confirms that the chine line rises above the waterline at the stern, leaving the waterline 'under' the hull and leaving the after edge of the running waterline to the shape of the bottom at this level.

http://i383.photobucket.com/albums/oo273/kevinmorin_photo/Titan%20Tug/SternStep_1a.jpg

Here is a little 14'er shown in various views to help make her more clear. The step I've referred to is the 90 degree pair of plates at the waterline under the transom. The vertical plate is at 90 to the bottom, and the horizontal is the bottom curve of the 'rounded' or curved transom.

http://i383.photobucket.com/albums/oo273/kevinmorin_photo/Val14/14_4a.jpg

This photo will be confusing if you don't look carefully as its not well taken or prepared to post. The skiff in the green model just above this image is being built. The stern is curved not fully rounded, and the transition step is shown. The problem in the the photo is that he female jig holding the bottom's shape has a straight edge stiffener at 90 degree to the aft most transverse former. This shows as a vague gray line, instead of clearly, but the bottom's section is visible farther forward where the shape is more distinct because of better contrast. You can see the after seam, curved; and you can see the horizontal transistion seam tacked too. What is hard to see, and I dont' have a better pic, is the lower seam of the step piece(s) that is where the vertical piece meets the hull bottom. This line is just barely visible at the upper corner (starboard) just near the chines.

http://i383.photobucket.com/albums/oo273/kevinmorin_photo/Lori/portside_nopaint_a.jpg

the method works for fully rounded sterns as well. This shot shows a full round stern on a skiff that has the transition step well under the bottom. An outboard T bracket in common to the bottom plane so the image is not exactly informative of the idea but just here to confirm that planing shapes that move at good speeds can have rounded sterns so they handle well in following seas at slow speeds but they don't lose anything at full speed.

again, I don't advocate this in wood since I've only done it metal, but I've done for nearly 35 years so I'm also pretty sure it works as shown. I hope this explains what I meant by a step at the stern to convert from a planing bottom to a counter/curved/rounded/fan tail stern?

cheers,
Kevin Morin

[PAR]

All those shapes can be handled in wood and commonly are. Looks like nice work Kevin.

[Deadrise13]

Kevinn nice work!! Thanks for all the input. Very informative, Do you have any examples of larger boats? I would love to see more. Thanks again----

[ancient kayaker]

Hm. Stitch and weld! Nice work!

[Deadrise13]

Hey Par, Never heard back from you!!! Hope all is well-----G-----