Where's that thread on PT boats? Been looking all over for it. And yes I used the search.
[ 01-21-2003, 01:27 PM: Message edited by: Buster ]
Where's that thread on PT boats? Been looking all over for it. And yes I used the search.
[ 01-21-2003, 01:27 PM: Message edited by: Buster ]
Dang it, there were numerous PT Boat threads and I can't find a one neither. Maybe we ain't using the search thingy correctly. Loon posted some great info on PT Boats in the past. This is a pretty good website to look at until he checks in.----> http://ourworld.compuserve.com/homep...m/ptboatp1.htm
Were you looking for something specific or just general info?
Peace---> Kevin in Ohio
My understanding was that it was the same basic hull shape, deep-V bow tapering to a flat stern, that many pleasure boats use, but that either because of length or weight it never planed and was a bad shape for that size boat. Wonder what a good shape would be for a long, heavy wood powerboat?
[ 01-21-2003, 03:57 PM: Message edited by: Buster ]
Member #1938
Here's another site that Kevin posted some time back...lots of good links on PT's
ptboats.org
By the way, I'd like to know how those 50 ton boats were able to do nearly 50kts, without planing.
Member #1938
Here's a 2 page thread, which not only has alot of links to PT boat sites, but a liberal dose of Classic Cleek as well. ( Or would that be a conservative dose?)
oops link
[ 01-21-2003, 03:30 PM: Message edited by: LOON ]
I think it had something to do with the V-12 PackardsOriginally posted by LOON:
By the way, I'd like to know how those 50 ton boats were able to do nearly 50kts, without planing.
I was gonna go back to that thread and it just sort of disappeared. The Germans expected 40 knots with one engine for their E-Boats and found they needed two. That rooster-tail in the old war movies says "bad design", and also, what? - that the prop is too high? I guess I'm looking for more information on planing, there must be a weight limit. Or is there? When a carrier goes full speed, is it planing? Now that would be something to see!
Member #1938
Senior Member
There was a recent thread about high speed patrol craft for sale in WB.
Custom Yacht Designs
Buster, I think that there is a good book or two able to be written to attempt an answer to your question. Lord (the other one, not Lindsay) knows we've been trying to answer it for about a century now. We designer types seem to have the basics down, but the devil is in the details so variations abound.
In the book, "Huckins - The Living Legacy", there is a description of the design competition that resulted in the WW II PT boat hull form. This was the seed of the Huckins "Quadraconic" hull form, and in the trials performed by the US Navy, the Huckins hulls out-performed those of Elco and another competitor (whose name eludes me right now). Production PT boats by Huckins, Elco, and the other contracted firms were all variations on Pembroke Huckins' design. Huckins went on to refine the hull form and it became the basis for most of their boats for the next forty years. They recently introduced a "retro-yacht" - the Huckins 44 - with this hull form. The first production hull is below:
The hullform is characterized by deep, concave sections at the bow transitioning to a flat transom. And I do mean flat! It is a perfectly straight line from chine to chine across the transom. In calm water or small chop the hull works very well and makes for a very dry ride due to the shape of the bottom throwing spray out and down. However, in larger waves when the boat begins to hobby-horse due to cyclical wave pressures, and at higher speeds where more of the bow is carried clear of the water surface, the hull takes wave impacts farther aft where the hull is flatter and this makes for a rather rough ride. At very high speeds in rough water, conditions that a PT boat would ordinarily encounter, these slamming loads were high enough that crew injuries and structural damage to the hull was reported.
The problem was that the sharp knife-edge of the forward keel area and forefoot sliced through the oncoming wave with impunity, throwing what water it encountered aside with aplomb, but did nothing to provide buoyancy to the hull as it attempted to traverse the wave. As the hull entered the body of the wave, the shape of the concave sections created buoyancy very quickly, resulting in a violent slam as the full momentum of the boat encountered the brunt of the wave. A better hullform for speed in a seaway was needed.
Along comes C. Raymond Hunt in the late 'fifties with just that "better idea" and applied the idea in 1960 in the form of a boat for Richard Bertram called "Moppie". He hit upon the idea of having the hull sections convex forward rather than concave, and tapering to nearly flat at the stern, but with a pronounced "vee" in the aft sections. Spray was controlled by fitting small spray strakes that knocked the spray down without presenting a flat surface large enough to create slamming. The convex sections created gradually increasing buoyancy as the hull entered a wave face, causing a much softer ride while the flat after sections provided an efficient planing surface for high speed. Planing hulls have been pretty much following this form ever since.
Once the hullform was developed that minimized slamming loads, the quest for bigger and faster began in ernest. With ever increasing speed and it's associated skyrocketing loads on the hull skin, construction materials soon became the Achillies' heel of fast, large boat design. Traditional plank-on-frame construction just wasn't up to the task. Initially there were variations in wood construction such as batten-seam, double-diagonal, and hot-moulding to try to overcome the problems of caulking being ripped out of seams, fasteners being sheared off, planks and frames breaking across the grain, and many other problems. Eventually it became clear that for the really high bottom loadings of large and/or fast planing hulls, another material was needed. Aluminium was ideal, but expensive and it required skilled craftsman to work. Fibreglass entered the scene and was the right product at the right time - rigid, cheap, and easy to produce with semi-skilled labour.
Now back to your question - what shape for a long, heavy wood powerboat? Hands down, the answer is a convex, deep-vee hullform similar to the larger Cigarettes and Fountains. How deep the vee should be is a function of the speed and sea conditions that the boat will operate in. The question to be answered is how strong and of what construction method to build the hull, the answer to which is dependant on how long the hull is expected to last and how deep are the pockets of the client.
As a brief aside, Ray Hunt was interviewed by a powerboat magazine and asked what were the qualities required by a designer to become the pre-eminant designer of an entire generation and creator of the most profound breakthrough in hull design in fifty years. His reply was wonderfully self-effacing and to the point:
"Nothing special. Just be there first."
Hope for the best, but plan for the worst.
Senior Member
WB had an extensive feature about the PT boats over a couple of issues. I'll check when I get home from work.
Elite Invisible Member
Donn I love that photo. Boy I sure would like to get a ride in one of those.
Chad
There are three ways to do things: The right way, the wrong way and my way.
Three Little Birds Love is My Religion
Member #1938
Thanks for the explanation, MMD. The other major builder (2nd to ELCO), was Higgins.
MMD.....Great informative post and it goes along way towards answering Busters question. I believe Higgin's was the 3rd builder of PT Boats Eh?
Peace---> Kevin in Ohio
[ 01-21-2003, 04:57 PM: Message edited by: Mr. Know It All ]
Member #1938
"Production PT boats by Huckins, Elco, and the other contracted firms were all variations on Pembroke Huckins' design."
According to this site the early ELCO's were based on PT-9, a British Scott-Paine design boat.
Elite Invisible Member
Still, all I want is a ride.
Chad
There are three ways to do things: The right way, the wrong way and my way.
Three Little Birds Love is My Religion
Those PTS aren't planing, Loon, but they're thinking about it. A little less weight aft and some trim tabs and up they'd come I'll bet. Thanks, mmd, that was interesting. How about some pictures illustrating the shape you described? The owner of the place where I work just bought a Fountain at one of those DEA sales ("Get A Porsche for $100!"). They found some bullet holes below the waterline. The Fountain is obviously not my type of boat, but they make good neighbors on the water because, as I mentioned in another thread, they leave virtually no wake.
Is a planing boat ipso facto somewhat unstable? My boat is prone to yawing at about 25 mph, which can be pretty hairy if you overreact. Thought it was because I have a very slight hog in my keel, but talking to coworkers about their glass boats I now feel it's the nature of the beast. Of course, anyone who wants to go fast through rough water is an idiot, unless he's in combat!
Someone offered my father a brand new PT boat in 1946 for $750.
Senior Member
I would like to reiterate a point that I hope I made in the last thread "Is there a ratio?" in Misc Boat Related.
The design conditions of a US PT, a British MGB, an Italian MAS, and a German E-boat were all different, so different hulls resulted. The massive weight and moment change traded off against sea speed required by a PT is inconceivable in modern yacht design. Even the picture of early Elco boats posted by Donn does not show the additional armorment added to these boats in the combat theaters.
Remember, a heavier V-bottomed boat has a smoother ride than a lighter one, though the peak skin pressures may be higher. Additionally, PT's spent most of thier time at idle, and only used max speed in the attack or to egress after expending their weapons. There is no moder pleasure boat requirement to meet these design conditions, except in the "small package trade". [img]tongue.gif[/img]
Very different take on the Huckins design on that ptboats.org site. According to them Huckins made only 18 boats and none were used in combat.
Custom Yacht Designs
Donn, the statement "The designs ... were all variations on Pembroke Huckins' design.." came from the Huckins book, and could be self-serving. From photos of PT boats of the era, it seems to be a reasonable assumption, but I am not enough of a historian of the boats to say that it is difinitively so. I do know from photos of the trials that the Elco & Higgins (thanks for the correction, all! [img]smile.gif[/img] ) hulls were significantly different that the Huckins, and that the production boats shortly thereafter bore a striking similarity to the Quadraconic hullform. I can only assume that the US Navy adopted what it felt were the best features of the three contestants and blended them into a hybrid for the commissioned boats.
Buster, I regret to say that I disagree with you on whether the PT's in Donn's photo are planing. They are, just not on a very efficient planing angle. This is a function of the shape of the planing surface and loading of the hull, and very nicely illustrates my comment about where on these hullforms the impacts of encountered waves occur at speed.
You asked re: picture to illustrate the shape I described - are you referring to the "Moppie" type of convex , deep-vee hull?
No, a planing hull is not inherantly unstable, but they can become so at certain speeds due to their hullform and centre of gravity. As each hull is different, the stability (in all axes; roll, pitch, yaw, surge, and heave) characteristics vary from hull to hull. There was an excellent article in Marine Technology (the organ of the Society of Naval Architects and Marine Engineers - SNAME) a few years ago on this topic, as well as an article in Professional Boatbuilder, on planing hull dynamics. I'll have a peek in the ol' archives to see if I can come up with one or both.
At risk of speaking too soon, before I re-acquaint myself with the problem's causes, I think that your yawing problem is probably caused by some minor longetudinal dynamic instability of the waterflow over the hull at speed. Pressure would build up on one side of the hull to a point where it forces the hull off-line, whereupon the pressure vents and the hull returns to it's original heading. The momentum of the return yaw allows the hull to continue the correction past the point of equalibrium, setting up the pressure differential on the other side of the hull. This is exactly the problem that makes poorly-faired dinghy rudders vibrate - the only difference is the frequency of the occilation. This yawing occilation occurs at a natural frequency of the hull until some external force - a wave or a steering correction, for example - overpowers the yawing force and either corrects it or throws it wildly out of control. I suspect that the yawing stops with very minor changes in speed - am I correct?
Possibly the addition of very small 'fins' on the hull bottom about 25% of the LWL forward of the transom, exactly parallel to the hull centreline and about 1/4 of the WL beam out board of CL, will cure the problem by overpowering the yawing moment. A 1" x 1/8" x 12" T-section of aluminium or stainless steel with rounded leading edge and square trailing edge might do the trick. Experimentation with fin length and longitudinal location will locate the optimum size and location. If I were to try this fix, I'd put them on with 5200 first and accept that they will rip off in pretty short order, but that they will probably stay on long enough the show whether or not they will work. If available, I'd use a stiff plastic T for the experimentation phase to minimize the risk of damaging your prop as they part company with your boat. If the test is positive, then a final, metal, set can be permanently affixed. No need to put screw holes in your boat for no reason.
John H. is spot on with his comments on that varying loads of combatant vessels. It is not unreasonable to expect the port departure weight of a PT boat to be double (or more) than that of port arrival, due to the delivery of ordinance and the huge amount of fuel carried. In contrast, a cruising powerboat may vary by only 15% in all-up weight between these two conditions.
Hope for the best, but plan for the worst.
43.50.918 N, 69.38.583 W
Also from the Huckins book: "We (Huckins Corp.) effected a contract with the Secretary of the Navy, dated July 10, 1941, licensing the use of the Quadraconic form of hull in consideration for a payment..."
The "Plywood Derby" took place on July 21-24, 1941, and in June of 1942 (after Elco had competed with their Scott-Paine inspired design), Huckins goes on to say,
"A miracle had occurred. The underwater form of the Elco underwent a metamorphosis, from the flat, pounding, runabout type of the Vee Bottom of Scott-Paine design to a shape miraculously resembling that of the Huckins Quadraconic hull."
The navy never paid Huckins any royalties on their design.
Maybe they could have used Steve Paskey's services.
“So we beat on, boats against the current, borne back ceaselessly into the past.”
Now this is the forum at its best! Thanks a lot! It's not really a problem - at least when I'm at the wheel - because that's about as fast as I want to take this old hull anyway. It's easily corrected with a slight reduction of speed and light touch on the wheel. The yawing seems to occur when the boat is running with the current or wave patterns; the lateral action of the water seems to have a greater effect than if it is running at a slight angle to the flow, I think. It's a 40-year-old hull so I guess I can forgive some idiosyncracies; a deep V at the bow tapering to a very shallow V at the stern. Is it safe to say that a small wake is a sign of efficient hull design?
It took some tweaking to get this boat to plane, but when it lifts it's quite noticeable. The angle changes, the speed suddenly increases, and the engine smooths out. Some of those boats shown in the ptboats.org site looked like they were running nice and level, but I guess like you said you can't really expect any boat so heavily laden to lift. Why did they use wood instead of steel?
[ 01-21-2003, 11:12 PM: Message edited by: Buster ]
Custom Yacht Designs
Ach! Me head! The questions are coming so fast!
1.) Pembroke Huckins was said to be quite angry when the majority of the PT contract was given to Elco and he received only a small fraction of the order.
2.) Yes, a small wake is indicative of good planing form.
3.) Steel was in short supply, so other materials were specified for the PT boats. Also, technology of the material and it's construction of the time made steel small boats quite heavy.
Hope for the best, but plan for the worst.
Senior Member
Several of your thoughts are very interesting but I will comment on one that occured during some towing tests that I made. I used a towing bridle attached to the center of buoyancy of the 4 foot model to allow the model to react with a minimum of restraint by the tow line. The model is of a hard chine planing hull scaled down from 24 feet. The model was designed so that the aft planing sections could be varied from a monohedron (constant deadrise sections) to a warped form in increments all the way to a flat transom.Originally posted by mmd:
No, a planing hull is not inherantly unstable, but they can become so at certain speeds due to their hullform and centre of gravity. As each hull is different, the stability (in all axes; roll, pitch, yaw, surge, and heave) characteristics vary from hull to hull. There was an excellent article in Marine Technology (the organ of the Society of Naval Architects and Marine Engineers - SNAME) a few years ago on this topic, as well as an article in Professional Boatbuilder, on planing hull dynamics. I'll have a peek in the ol' archives to see if I can come up with one or both.
At risk of speaking too soon, before I re-acquaint myself with the problem's causes, I think that your yawing problem is probably caused by some minor longetudinal dynamic instability of the waterflow over the hull at speed. Pressure would build up on one side of the hull to a point where it forces the hull off-line, whereupon the pressure vents and the hull returns to it's original heading. The momentum of the return yaw allows the hull to continue the correction past the point of equalibrium, setting up the pressure differential on the other side of the hull. This is exactly the problem that makes poorly-faired dinghy rudders vibrate - the only difference is the frequency of the occilation. This yawing occilation occurs at a natural frequency of the hull until some external force - a wave or a steering correction, for example - overpowers the yawing force and either corrects it or throws it wildly out of control. I suspect that the yawing stops with very minor changes in speed - am I correct?
The model performed well at all speeds in the monohedron form but when the shape was changed so that the transom deadrise was about half the midships deadrise, a yaw condition was set up. As I increased speed, the model began to yaw violently and eventually did a 180 and tore up the towing rig.
My conclusion was similar to yours. I suspect that the circular wake generated by the hull warp induces a steering moment to the transom. As long as the moment is small and/or both sides balance and no outside influence disturbs it, the model runs true. At higher speed and the hull encounters an asymetric wave (aren't they all), the hull will roll and one side of the aft bottom will get a bit more reaction to the induced wake than the other. If the stimulous is near the natural frequency of the hull (at the time), a yaw is set up. If the unbalance is strong enough and it is not damped out, it will result in the foundering that I saw.
The addition of fins or skegs as you suggest would likely either damp out the yaw or move it to a higher speed range. In my case, I chose to use the monohedron hull form that shows much higher resistance to the yaw problem.
I want to get back to more model tests but they are very hard to do accurately and I have just not gotten around to it.
Anyway, the discussions here have been highly interesting in the last week or so with more valuable thoughts and explanations being shared than at any other time in my experience.
And yes, those PT boats are definitely planing. I think a thread strictly about planing would be very good.
Tom L
Sorry, you opened up this font of knowledge and I'm going to tap it for all I can get.
Member #1938
Buster...you think PT's are interesting...search the forums and Google, for rumrunners and Liberty engines.
There was a show on Discovery or TLC a while ago about them. One yard in Long Island was building rumrunners on one side of the yard and coast guard interceptors on the other.
Member #1938
The two guys who designed my boat did that very thing.
Custom Yacht Designs
Tom L. - Thank you for joining the discussion. You are much farther ahead on the curve than I; that you have taken the opportunity to perform model testing places you in a different level of experience than I. My best defence is that all the planing hulls I have designed to date have performed up to calculated expectation, the caveat being that I have not explored the outer fringes of the medium - yet.
What was the intended use of the hull you tested, if anything other than pure research? Did you perform numerical analysis of hull resistance prior to testing for comparison to the model data? Were you able to ascertain from the tripping and subsequent roll-over of the hull if the tripping occurred on the forefoot of the hull or on the chine? Sorry to be such a jabberwock of questions, but as I have blithely said in other posts, enquiring minds want to know!
If you would like to pursue your suggestion to have a thread on planing hulls, I will most certainly follow you there. Maybe a start would be to (if I may be so bold) open the thread with a brief description of your test hull in terms of my questions above.
I do so like it when the forum gets to the nitty-gritty of what makes boats work.
Hope for the best, but plan for the worst.
Senior Member
I started thinking about a small cruising powerboat after retiring as an electrical engineer and having experience primarily with sailboats and no real design knowlege. I am still very much an amateur but just naturally applied the normal design principles that I learned in engineering design. That is, to set down the design objectives, learn enough to eliminate incompatibilities, prove the concept and then build it. I'm an analog thinker and try not to get bogged down so that the mathmetics obscures the basic principles.Originally posted by mmd:
Tom L. - Thank you for joining the discussion. You are much farther ahead on the curve than I; that you have taken the opportunity to perform model testing places you in a different level of experience than I. My best defence is that all the planing hulls I have designed to date have performed up to calculated expectation, the caveat being that I have not explored the outer fringes of the medium - yet.
What was the intended use of the hull you tested, if anything other than pure research? Did you perform numerical analysis of hull resistance prior to testing for comparison to the model data? Were you able to ascertain from the tripping and subsequent roll-over of the hull if the tripping occurred on the forefoot of the hull or on the chine? Sorry to be such a jabberwock of questions, but as I have blithely said in other posts, enquiring minds want to know!
If you would like to pursue your suggestion to have a thread on planing hulls, I will most certainly follow you there. Maybe a start would be to (if I may be so bold) open the thread with a brief description of your test hull in terms of my questions above.
I do so like it when the forum gets to the nitty-gritty of what makes boats work.
At first, it was an academic exercise since I had no real confidence that I could develop a boat to do what I wanted. There were plenty of local boating kibitzers who shook their heads at my proposal to build a cruising boat that would plane comfortably and economically at double sailboat speed (10 to 12 knots). None of the boats on this coast will do that and they all said that I would need at least double my intended 50hp to get a full size 24 foot boat up on plane anyway.
Over several years of fits and starts and studying the sparse literature available and understandable to a layman, I had a design and built the model. I did not do scaling of forces although I did measure total resistance and compared that to what I could find in books. Mainly I studied Lindsay Lord, interpolated and then applied his recommendations.
The process was far too long to put into a few words and I doubt that my "expertise" exceeds that of most who have commented here. Maybe different but not necessarily more informed. The yaw I spoke of resulted in the model swapping ends and not in rolling over.
The model was used mainly to study behavior in different sea states under different bottom configurations and weights from -20% to +80% of projected displacement. The tests plus discussions with a boat designer friend gave me some confidence. At that point it was S*** or get off the pot so I ordered the plywood and was forced to get on with it.
The boat has been on the forum before and can be seen at:
http://www.messing-about.com/
and more at:
http://www.messing-about.com/smallboats/bluejacket.htm
This is by no means the end all of cruising boats but it satisfies all my original goals and suits us really well.
This is by no means the end all of cruising boats but it satisfies all my original goals and suits us really well.
[ 01-21-2003, 11:35 PM: Message edited by: Tom Lathrop ]
Tom L
Senior Member
I worked at Electric Boat in Groton CT briefly back in 1964. There was a retired Chief in my section who owned a PT; he'd picked it up at auction somewhere in the 50s (cheap) after being tipped by some buddies that it was available. I don't know the number or builder, so which type is something I can't say.
All armament and electronics were stripped (naturally) but the 3 engines were still present and in good shape. He reworked it roughly into a 'pleasure' boat. Said he saved for several years to get enough money to gas it up 'sufficiently', then spent a glorious afternoon running up and down Long Island Sound with the cutouts open - he said it would do about 60-65 mph with all that weight stripped out.
Then he sold 2 of the engines; and it would STILL do just over 50...
Custom Yacht Designs
Tom, what is the angle of the planing surface (vee) at the transom, and how far does it run forward at that angle?
Just as a "fer instance", this is a low-angle planing hull that I designed for a lobster fisherman who wanted to go fast. The boat is an aluminium 36-ft LOA and does about 33 knots with a 350-hp Caterpillar and an UltraJet jet drive. Same as your monohedral hull, there is no noticable bow-up "hump" as it gets up on plane - just a smooth, level transition from displacement to planing.
Hope for the best, but plan for the worst.
Nice. What kind of mileage is he getting?
Custom Yacht Designs
Sorry, Buster, but we never work it out to MPG. We look at the load cycle of the engine based on percentages of use at various RPM levels to get an average GPH and then size the tanks to match the range that the client wants. We look at the distance from dock to fishing grounds (full throttle), then the average time working the traps (1/4 throttle), calculate the average GPH based on fuel consumption curves supplied by the engine manufacturer, multiply the result by how many trips the fisherman wants to take to his fishing grounds between fuelling up to get the required tankage volume, and add about 10% reserve capacity. From this number we calculate the tank size and range of the boat. The bottom line is that fuel economy is measured in GPH, not MPG.
Hope for the best, but plan for the worst.
Senior Member
mmd; the forgotten manufacturer was Higgins.
Couldn't you extrapolate mpg from gph? I'm going to try a bow tank this year to see if that encourages planing. And it might be a bladder in a cradle.
Custom Yacht Designs
Buster, adding weight to the bow will not usually encourage planing unless your boat has a tendency to squat by the stern when on plane, like the PT boats in Donn's picture. Usually, moving weight forward will keep the bow down when the hull tries to get over the displacement bow wave and get up on full plane, causing a larger bow wave to overcome and increasing the wetted surface of the hull, adding frictional drag. Also, when on plane, if the planing angle is too low relative to the chine line, the hull is more prone to dynamic instability such as tripping which will cause a violent and unpredictable turn at speed. If control of your boat's planing attitude is your goal, you will probably be better off with trim tabs rather than adding bow weight. If you are certain that you want to add weight forward, might I suggest some experimentation with sandbags forward before you go to the effort and expense of fitting a tank?
Finally, please reconsider using a bladder tank for fuel. I fear that you are about to create something that is quite dangerous.
P.S. - yes, one could extrapolate MPG at various RPM's, but it would not account for headwinds, tidal currents, waves, etc. As most navigation - even with GPS - is based on elapsed time, it is more accurate for the boat operator to think in terms of GPH. Fewer surprises that way.
[ 01-22-2003, 09:34 AM: Message edited by: mmd ]
Hope for the best, but plan for the worst.
Good idea. I thought getting on plane was about lifting the stern.
http://www.atlinc.com
So what would the hull shape be on a modern 80-footer going very fast and heavy through rough sea?
Senior Member
Think aircraft or submarine.Originally posted by Buster:
So what would the hull shape be on a modern 80-footer going very fast and heavy through rough sea?
Like the Pony Express, modern technology has overtaken the design need for a small high speed power boat. What's left are an individual owners wants, so how deep are your pockets to pay for a new design evolution? Most people are content with the current state of the art as few ever will be out going high speed in more than moderate conditions. Seaknife, SWATH, SES, high speed cat, tri-hull thin ship, hydrofoil, etc. there are many designs and they all come with trade-offs and costs. If it was me, I'd look to something like the TRITON R&D platform or SES-100.
Posting Permissions
Reply With Quote