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Stretching Ocracoke 20, 24 or 256 in length only


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I love the look of the Ocracoke series/ Carolina hulls, but I am looking for a boat with as little "hump" as possible as the boat speeds up. The reason being is that I want a hull that is efficient at 8/9kts (this is a speed we troll lures at a lot) but I also want a boat that can  plane/ rum some distance - though top speed is not particularly important to me. Say a cruising speed of 20kts or so and a max of 30. 

 

The closest hull that we have come across that can do this is a Panga style hull. 

 

A few questions:

 

1) Could Ocracoke series be stretched in length by a few feet (I am guessing by changing the spacing of the framing)...

 

2) Would this have a positive impact in the tradition between low speed and planing... and would the hull be more efficient at say 8/9kts...

 

Again - top speed is not that important and neither is having more "beam" although at a certain point, I understand that the aesthetic of the hull as a "Carolina hull" would change ...

 

 

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You have raised the age old dilemma, how to beat the hump. It is something that I have been struggling with for most of my working life. I do not think that we will ever see $2.50 a gallon gas again, so it is worth thinking about.

 

The best approach is to go longer as you suggested and lighter. You can space out the framing to get longer. You can also add the outboard bracket. The bottom of the bracket sits a couple of inches above the transom and pitches up aft so that it does not drag while planing but lengthens the WL in displacement mode.

 

It is hard to make the boat much lighter but you can pay attention during construction to not add anything unnecessary and choose okume ply over heavier species and not going above a 90 hp motor. Just by lengthening the boat and adding the extra structure you will end with a lower displacement to length ratio because it is a function of weight in long tons divided by .01 WL cubed, therefore it will be lighter for it's length. 

 

Trolling at 9 knots on the standard Ok20 with it's 16' 4" WL gives you a speed/ length ratio of 2.2. If you had an effective Wl of 25' your S/L R is 1.8. Is it worth it? If you spend enough time at this speed, it probably is. 

 

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First off I am not a professional designer and never play one on the internet.  And I surely will not suggest any modifications on any current B&B designs. But with that said now, I will relate my experiment on this very topic, which hits me directly in the forehead when I built my current 19 skiff. My skiff is 9 years old now and has a lot of water under its keel in that time.  Its a traditionally framed skiff planked in lapstrake. The skiff weighs with the engine on it rigged for fishing at around 1,100 lbs. 

 

The engine is hung on a traditional transom instead of a bracket, where your deadweight is hung further aft without any bottom in the water for support.  When i was considering the build I did not want or consider a big engine, but a 60 hp, 229 lb four stroke. 

 

I only carry a six gallon fuel tank too. I started my narrowing of the waterline beam further aft than I normally would have  when considering how the boat would handle  down sea. This pointed the bottom in my shallow draft boat longer to the bow.  It is a bit narrower than a normal boat in a simular size, but not as narrow as a Panga.  I did have the Panga in mind, but never wanted anything than narrow or shape. The constant nasty shallow water chop in our area has always been uncomfortable over the years.

 

So as my bride and I have aged, and we did not need a lot of room, we gave up some beam and modified the bottom in my point of view to deal with the slop. The boat is shallow draft, very dry and very comfortable at 20 to 22 mph and tops out at 29. 

 

Now overall we did notice that what I did  does remove some of the hump when starting out and trolls at a nice 9 to 10 mph flatter. If the weather is nice , when I get on plane, I just trim the engine up a bit and gain about 2 mph in speed on my cruise with less bottom in the water.  I also keep the nose up a bit when running downwind and under certain conditions I keep the trim up a bit more than I do when I normally set it at when running in smooth water. 

 

As a side note there are some of the larger sportfishermen that the designer is aware of, one being a Jim Smith and a spin off being Kirkline that has a different shape to the chines starting at the transom that changes and increases the deadrise from the transom, which makes them run flatter too. especially the Kirkline.

 

 

 

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6 hours ago, Designer said:

You have raised the age old dilemma, how to beat the hump. It is something that I have been struggling with for most of my working life. I do not think that we will ever see $2.50 a gallon gas again, so it is worth thinking about.

 

The best approach is to go longer as you suggested and lighter. You can space out the framing to get longer. You can also add the outboard bracket. The bottom of the bracket sits a couple of inches above the transom and pitches up aft so that it does not drag while planing but lengthens the WL in displacement mode.

 

It is hard to make the boat much lighter but you can pay attention during construction to not add anything unnecessary and choose okume ply over heavier species and not going above a 90 hp motor. Just by lengthening the boat and adding the extra structure you will end with a lower displacement to length ratio because it is a function of weight in long tons divided by .01 WL cubed, therefore it will be lighter for it's length. 

 

Trolling at 9 knots on the standard Ok20 with it's 16' 4" WL gives you a speed/ length ratio of 2.2. If you had an effective Wl of 25' your S/L R is 1.8. Is it worth it? If you spend enough time at this speed, it probably is. 

 

Thank you for your very kind and detailed response. I suspect it must be frustrating as a Designer when some layman wants to start altering your carefully designed works of art!

 

We typically would run for less that 1.5 hrs per day total and troll for 6 - 7 hrs at 8-9 kts - so any savings at that speed would be considered a real bonus especially with rising fuel costs. I have always been amazed by the amount of fuel that a small trailer boat can use at these speeds - when compared even to say a large (albeit diesel) inboard sport fisherman. I am no boat designer, but have often wondered whether a part of this is because a large sport fishing boat over say 36 feet is still within is "hull speed" at 8 kts; vs a trailer boat where you essentially are spending all day driving it "uphill" at those speeds!

 

With this in mind, could I ask a couple more questions on this subject?

 

1) I understand that there are compromises on the weight as well that effect the efficiency - but would it maybe make more sense to stretch the OC 24 (not the OC 20) as much as structural/ aesthetic parameters would allow? 

Boat would typically have 4 men on board, with fishing gear, but minimal clutter. No head etc.

 

2) What would you Consider acceptable to stretch your OC plans by? Aesthetically, I feel like one could add 25% and still have a very handsome boat - far more beautiful than a Panga - that would still retain some "Carolina" lines. I don't know what you would consider acceptable from a structural/ design point of view?

 

3) Would you be comfortable "keeping a watchful eye" on a builder who did this having purchase the appropriate plans?

 

3) Is the "transom bracket" considered "free length for the weight" at displacement speeds ? In other words, were one to stretch a hull to the same length as a bracketed hull but keeping it "full" all the way, then would one then need to increase the scantlings/ structure of this hull - and thereby increase the weight and reduce efficiency?

 

4) Are there any major disadvantages (other than aesthetics) to a longer leaner hull that one is not planning to run at excessive speeds? (As I understand it many boats have evolved more beam to carry larger engines/ and or fit more amenities into a shorter hull). I guess what I am asking is, will a 28 foot boat with an 8 foot beam behave very differently in terms of stability/ planing characteristics than a 24 footer with an 8 foot beam?

 

5) Are there other "tricks" a designer could employ (as suggested by Oyster) that might trim the boat more level? Wider chine flats? A different hull form?

 

The noticeable growing popularity of the Panga style hull in the US must speak something about the rising prices of fuel/ their sea-worthiness/ practicality - which it would seem poor third world fisherman have long known/ admired. I have never liked their lines, or low freeboard but have always been impressed by them as a fishing platform. 

 

 

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First off the Panga has a completely different bottom and draft than the boat you are considering. Its originally designed to be beached. The narrow beam works in the favor of riding in the big swells associated with the regions that they were native to.  Leaving the beam aside for the design, I never have felt or heard that the lack of beam was targeted directly as being able to use a smaller engine. In most of the areas that you see them, the boaters are not concerned about going fast. I can't speak about what the original ones weighs in a simular length, built in wood, so I would not really think about how a new build weight compares to the original Pangas. 

 

Of course in general, the narrower the beam, the less you may burn in fuel, with a lot of iff ands and butts. So I would not try to compare the two designs solely on fuel burn. Profile lusting happens to a lot of folks in their original search that ends up favoring a Carolina design. But last do not attempt to under power any boat for the sake of an idea of burning less fuel. Of course the larger the engine, the more you initially spend for your power. 

 

  There are a lot of instances of  putting the proper engine on a boat and not having to run it on the top end, yielding you less burn less fuel than an under powered boat and having to shove the throttles to the pins to get the running angle right too. You end up dragging tail. Of course  trim tabs are installed in a lot of under powered boats to get it to run decent and perform in a sea comfortably.  And when your get it rigged, your boat always gains weight too. Sometimes this happens to modify your performance.  Sportfish boats are not boats really designed around sipping fuel.  Each person has their own idea about what they budget on fuel. SO its hard for most of us to know that target. No two trips will yield you the same gpm. 

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On 6/21/2022 at 3:15 AM, Oyster said:

Sometimes this happens to modify your performance.  Sportfish boats are not boats really designed around sipping fuel.  Each person has their own idea about what they budget on fuel. SO its hard for most of us to know that target. No two trips will yield you the same gpm. 

From personal experience of 3 different types of boat I have fished in doing very similar outings - and repeated enough times in each boat to know that these numbers are "repeatable" ... a friend's 17 foot Mako with a 90 HP Etec averages 130 lts of gas burned in a day pulling blue Marlin Lures at 8-9 kts a 36 foot Hatteras (heavy and built in the 70's) with twin 300 HP diesel inboards burns about 220 lts of diesel, and a Yamaha Panga 23 with a 50 HP Yamaha 4 stroke will burn about 50 lts of gas in the same day. The Panga will almost always out fish the short "trailer boats" and will often do very well side by side the big "Sportfishing boats". I don't really have anything better to compare with than the above as to what a person's idea of fuel burn is, but logic would dictate that for the man not able to afford a large sport fishing boat, then all else being equal a Panga would be a better bet for trolling marlin lures than a short trailer boat.

 

Beaching and other functions of a Panga aside, I am curious to know whether simply stretching an Ocracoke enough in length would match these sorts of differences in fuel burn. I still think a stretched and narrow Ocracoke would be prettier than a Panga!

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My point as it relates to different fuel burns is not all trips are the same in time and the amount of fuel used, depending ona lot of factors.  Sea conditions changes your running rpm and even your fishing speeds. But no big deal,,

If I understand you correctly you are asking if stretching the Ocracoke will yield you a better fuel burn from the original.  Well naturally you are adding more weight when you stretch any original design. Will it make a difference? ??? Don’t know,  But you are trying to compare the design to a Panga that has no simular features in their design to the OK, which has an entirely different wetted bottom in the water for starters.  I don’t think anyone can give you a concrete answer to what you  are wanting. Of course this is really a question that the Designer can follow up.. Just trying to relate my own experiences and thoughts.. But for some reason no matter the design, its fairly common for people to want to change the plans , which can have some adverse affects after they are built and loaded. This is my personal observation. I will bow out now and just read. 

 

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This is slightly off topic. Core Sound 17 Hull #1 was built out of aluminum and the last time I saw it was on the beach with the Panga's at Puerto Vallarta on the Mexican west coast. The builder resides there and is one of those guys who usually out-fishes everyone around him. He reaches out and back under sail and usually comes back in after burning no fuel with more fish than the big gas guzzlers.

 

On 6/20/2022 at 7:00 PM, Johnnyfishes said:

1) I understand that there are compromises on the weight as well that effect the efficiency - but would it maybe make more sense to stretch the OC 24 (not the OC 20) as much as structural/ aesthetic parameters would allow? 

Boat would typically have 4 men on board, with fishing gear, but minimal clutter. No head etc.

 

Yes.

 

2) What would you Consider acceptable to stretch your OC plans by? Aesthetically, I feel like one could add 25% and still have a very handsome boat - far more beautiful than a Panga - that would still retain some "Carolina" lines. I don't know what you would consider acceptable from a structural/ design point of view?

 

25% is quite a stretch. It would turn her into a 30 footer plus a 4' bracket. I have been wracking my brain as to the best way to lengthen he boat without turning it into a whole new design which is why I have taken a while to respond. If she is stretched proportionally the stem rakes way out looking strange and the transom rakes 16.1 degrees.

 

3) Would you be comfortable "keeping a watchful eye" on a builder who did this having purchase the appropriate plans?

 

Yes.

 

3) Is the "transom bracket" considered "free length for the weight" at displacement speeds ? In other words, were one to stretch a hull to the same length as a bracketed hull but keeping it "full" all the way, then would one then need to increase the scantlings/ structure of this hull - and thereby increase the weight and reduce efficiency?

 

The bracket should increase displacement efficiency over a lengthen hull. It is hard to know at what point in the hump it would reverse. Probably but you are talking in the margins.

 

4) Are there any major disadvantages (other than aesthetics) to a longer leaner hull that one is not planning to run at excessive speeds? (As I understand it many boats have evolved more beam to carry larger engines/ and or fit more amenities into a shorter hull). I guess what I am asking is, will a 28 foot boat with an 8 foot beam behave very differently in terms of stability/ planing characteristics than a 24 footer with an 8 foot beam?

 

I like the idea. Longer boats pitch and pound and weigh less proportionally. Naturally they have less stability than their beamier alternative. I know someone who had an elevated helm station on a Panga and with he and a crew up up there, capsized it offshore. He currently has one of our boats.

 

5) Are there other "tricks" a designer could employ (as suggested by Oyster) that might trim the boat more level? Wider chine flats? A different hull form?

 

We already have chine flats that are as wide as we feel we can make them without them slamming.

 

The noticeable growing popularity of the Panga style hull in the US must speak something about the rising prices of fuel/ their sea-worthiness/ practicality - which it would seem poor third world fisherman have long known/ admired. I have never liked their lines, or low freeboard but have always been impressed by them as a fishing platform. 

Here is the fuel burn curve that I made for my OB20 with an Etech 50 showing the hump. I trimmed the boat out as best as I could at each speed and took the lowest GPS reading in flat water. I took the fuel/RPM burn from Etech's web site and have not had a chance to verify it yet. You can see that I do not get any better mileage at 9 knots than 18 knots. For a large 20 footer, she is fairly economical due a small engine and accepting a comfortable planing speed as my cruising speed weather permitting. She does have trim tabs which I like but she jumps out of the hole quickly without them. 

OB20 fuel burn.jpg

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Point taken regarding wind power and fishing! It has certainly worked for centuries! 
 

Also thank you for the chart.
 

Am I interpreting it correctly in assuming that the 6.5 kt speed seems (to me) strangely efficient with a fuel burn of 13 nm/ gallon? (The whole boat seems very efficient in that case). 
 

From a fishing point of view, this boat would burn twice as much fuel in a day fishing at 9kts vs 6.5kts (albeit it’s still pretty good to do a 10 hr day trolling on 40 lts (vs 20 lts at 6.5 kts)) 

 

I guess the question I am asking is how that 6.5 kts efficiency could be pushed to a slightly higher speed.
 

In marlin fishing there is a huge difference between 6.5 kts and 8/8.5 kts in terms of success and how well lures run etc. 
 

Would this hull stretched 25% in length only, and somehow keeping the weight similar, achieve this? 
 

In my terms I am measuring efficiency not as a measure of fuel burnt for a distance covered but in terms of maximising trolling time out of a certain amount of fuel at 8-9kts speed. 
 


 

(I do understand that this is a lighter hull design with a shallower deadrise than the OC series)… 
 

 

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Yes, you interpreted correctly. The caveat is, I have not had the chance to verify the fuel burn yet. 

Those low speed numbers bothered me too. Evinrude claimed that with 2 strokes firing twice as often generate more torque at lower rpm than 4 strokes.  

I took those numbers from https://www.boat-fuel-economy.com/inboard-vs-outboard-fuel-consumption

 

They show the Etech 50 burning .5g at 2000 rpm, Yamaha 50 .9g and Honda 50 .7g. and of course the performance was the best that could I tune in flat water but it gives some idea. The problem is interpreting apples with apples, we have to convert RPM to HP. The outboard makers do not release their torque/fuel burn curves like the diesel makers do. How much HP is each motor generating a 2000 rpm?

 

I found a way to stretch the OK24 to 28 feet and keep the same properties and fairness without having to do a complete redesign, except for the volume. The stem and most of the frames stayed the same. LOA 30'5 with bracket, LWL 26' 2".

 

Because the beam and height has not changed and displacement has not increased much,the scantlings do not change. There will be one new frame added and some readjustment of at least 1 frame.

 

To run 6 knots gives a speed length ratio of 1.17 which does not take much effort. 

 

Here are a couple of screen shots of the stretched hull. I hope dust off our performance prediction program next week  to see if we can get some realistic numbers. We have some real life numbers from a few OK 24's to help to dial it in.

 

OK2428 1.jpg

OK2428 2.jpg

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This is amazing - thank you for looking into this and I hope it is of some interest to you as well. It is my intention that this becomes more than simply the academic exercise it is at the moment - I would love to build the first stretched OK24!

 

As I said before it has always surprised me that offshore fishing boats which spend so much of their time trolling at this very inefficient 8 kt "hump speed" seem to have that so low on the list of "design priorities" - I guess when fuel prices were cheaper it didn't matter as much. Or perhaps when you factor in the typical usage - long runs off shore, bottom fishing, live baiting, slow trolling etc then trolling lures at this speed is not as much of a factor as I imagine.

 

I know that we can use up to 3 times the amount of fuel in a day between live bait fishing/ slow trolling at say 4 kts and lure trolling at 8 kts when in a small "trailer" boat. 

 

Hence some of my surprise at the OB 20 numbers. I would love it if your OB 20 is as efficient at those speeds as the chart predicts but they seem incredibly good numbers. 

 

The steady increase in interest in Panga's for the recreational boater (in the US) may well be a reflection of people feeling the pinch of fuel prices but I also feel like their attributes as great all rounders have long been held back by their less than beautiful looks. There was definitely a time when I would have sworn I would never be arguing the merits of a Panga!

 

I like the lines you have drawn a lot - and also that you have found a clever soln to the stretch -  but I have a couple of questions:

 

1) I am curious how much you think the bracket helps enhance the waterline length/ efficiency at trolling speeds? Or whether this hull would perform similarly with transom mounted engines? I quite like being able to pass rods over engines that are closer to the boat when fighting a fish.  

 

I can see their advantages in increasing cockpit space and also as a boarding platform - but am curious if they improve hull speed as well?

 

2) Would/ could one increase the beam and possibly height of the flare slightly to give the impression of a "beamier" hull whilst maintaining the slim underwater profile - or does this enter the realms of a total redesign and/ or affect stability?

 

I look forward to seeing some predictions when you get a chance. And once again many thanks. 

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