Do trawlers roll a lot?

psneeld · Jul 26, 2013

brian eiland said:
I'm having trouble defining exactly what the optimum 'displacement speed hull' is ??

As I looked thu that rather lengthy subject thread "Hull Shapes....show us your girls bottom", it appears to me that many different hull shapes can be operated reasonable well at displacement speeds. It's when they try to get above their displacement speed that they need a lot of tweeking.

I don't see where this general shape is that much different than the Grand Banks hulls, other than being a little flatter in the stern?

sure...ANY hull can be operated reasonably efficient at displacement speed..but it's pretty hard to water ski there....

I run the shamrock as an assistance tower...people aren't going to wait for me to show up at "displacement speeds"....

Underway · Jul 26, 2013

Here's what Ed Monk and some others have done to "soften" the roll reversal on a hard chine, semi planing hull. Theoretically also has the benefit of running on a narrower, lower drag hull when the boat begins to lift (I won't say plane) at higher speeds.

AusCan · Jul 26, 2013

brian eiland said:
Interesting posting Marin. I'm going to have to look up some more info on these hull shapes if there is not more discussion of them as I read thru this tread.

Another item I see yet to be mentioned is bilge keels? Do they work to limit the rolling motion?

Brian,
Our local waters are relatively unprotected and confused, and there is rarely less than 15-20 kts of wind. Typically about 6 ft of messy swell, so there aren't many recreational type trawlers. (only real ones) Deep vee hull Bertram 35's and the like are the most popular power boat for those who can afford the fuel.

I went for a full displacement hull which is shaped like a small Willard 40. Very efficient round stern, but the standard versions roll like a bitch in a beam sea. The manufacturer tried in minimise this on later models like mine by adding bilge keels, and from what I understand this helped a little. But still in a beam sea - its rock and roll time; soft and gentle but LOTS of movement. Hold onto your beer! I would say the motion is still very safe, but not at all comfortable.

Just before the company stopped production they released a few motor sailers. Once I raise my small sails (total 300 sq ft), its a totallly different story. Everyone aboard breathes a sigh of relief and you no longer have to wedge yourself in a corner.

Larger bilge keels may do more to slow the roll, (mine protrude anout 12" from the hull, and run about half the length of the WL), but in a bad sea and a very soft chine you need additional roll attenuation of some sort.

I went with the sails, rather than stabilizers/fish so I could add a knot or two rather than take one off, and have no regrets at all.

AusCan · Jul 26, 2013

Here's a pic showing the bilge keels.

Art · Jul 26, 2013

skidgear said:
Here's what Ed Monk and some others have done to "soften" the roll reversal on a hard chine, semi planing hull. Theoretically also has the benefit of running on a narrower, lower drag hull when the boat begins to lift (I won't say plane) at higher speeds.

View attachment 21674

Skidgear

That photo's chine area looks very similar to some Monk designed Tollycraft that were produced only for a couple years. Being in the Tolly Club I can attest that most owners of that hull design seem not too happy with its lack of stability in seas when anchored and I've heard complaints about its beam sea actions at trawler speeds as well as unpleasant hard cornering at higher speeds. At least two I've seen picts of while refit was underway; they filled in that "inverted, cupped chine" and brought the chine back into standard Tollycraft design conditions. As you mentioned, Monk's intent was less friction due to less bottom surface when a Tolly was on full plane... Tolly’s such as these had WOT speeds of 21 to 25 knots with factory power. If repowered with real meat I read of one that reached into the high 30’s!

Like I said in post # 150: “Every individual configuration in a hull WILL make it react differently with water it travels through and the sea conditions it encounters while traveling or at stand still; as well as speeds it travels,...”

Happy Boating Daze! - Art :dance:

brian eiland · Jul 26, 2013

AusCan said:
....I went with the sails, rather than stabilizers/fish so I could add a knot or two rather than take one off, and have no regrets at all.

Yes I've been a sailor all my life, and I understand them. Those sails can make all the difference.

...and I've had a life-long interest in motorsailers.

What I'm trying to do right now is understand power boat hulls,...that I have very little experience with. And I don't pretrend to be interested in the go-fast and planning powerboats, that's a whole different ballgame. I'm interested in what makes the ideal DISPLACEMENT-SPEED powerboat hull. And at this particular time a displacement speed hull for coast-wise, inland waters, not offshore work.

brian eiland · Jul 26, 2013

Brian said:
I'm having trouble defining exactly what the optimum 'displacement speed hull' is ??

I don't see where this general shape is that much different than the Grand Banks hulls, other than being a little flatter in the stern?

psneeld said:
sure...ANY hull can be operated reasonably efficient at displacement speed..but it's pretty hard to water ski there....

I run the shamrock as an assistance tower...people aren't going to wait for me to show up at "displacement speeds"....

So you agree with me that most any hull can be operated efficiently at displacement speeds. I was NOT asking about water skiing.

As far as the Shamrock hull shape is concerned I was suggesting that this hull shape might be expanded up to the ~40 foot size, and still be a reasonable hull configuration for a displacement operating trawler? Again I was not asking for a fast boat shape that your people are not wanting to wait for.

Art · Jul 26, 2013

AusCan said:
Here's a pic showing the bilge keels.

AusCan

You’ve got a cool designed boat w/ nice looken bottom!

Bet she economically and smoothly slips through the water nice and quiet at hull speed while sitting fairly upright at anchor as wakes come broadside. Beam sea action should be dampened quite a bit by the side keels. Following sea would only be problematic if you've not enough power/speed to keep up with the waves and the rollers roll up on/against/under your stern... but, it also looks like she has a rounded soft stern to let the rollers slide underneath, if necessary. Hitting a head sea should be no problem as she has a fine flair at her prow and the superstructure looks to have ben planned to handle some rough encounters. Her general shape/design reminds me of some real nice New England coastal seagoing boats I became accustomed to in 1950’s - 70’s.

Am I reading your rather small photo correctly! It won’t punch up and enlarge for me... but I did blow it up another way, although it became blurry.

AusCan · Jul 27, 2013

Sorry Art. I don't have much for pics here on my work PC, but here's a slightly better one. The black hull still doesn't show the lines well in a photo, but she certainly is slippery.
It loves a following sea. I've surfed some big waves coming in to our marina, at she does it with style. No hint of broaching so far.

The bilge keels don't do as much as I expected to stop the rolling in a beam sea. She stays perpendicular to the water, but when the swell is big, that doesn't mean upright.

When the seas get confused, with short messy swell, the sails become a necessity. It works well for the consistently windy local conditions.

Art · Jul 27, 2013

AusCan said:
Sorry Art. I don't have much for pics here on my work PC, but here's a slightly better one. The black hull still doesn't show the lines well in a photo, but she certainly is slippery.
It loves a following sea. I've surfed some big waves coming in to our marina, at she does it with style. No hint of broaching so far.

The bilge keels don't do as much as I expected to stop the rolling in a beam sea. She stays perpendicular to the water, but when the swell is big, that doesn't mean upright. When the seas get confused, with short messy swell, the sails become a necessity. It works well for the consistently windy local conditions.

FUN BOAT!!

Congrats!

One of the nicest I've seen on TF...

Al · Jul 27, 2013

Greetings- In an earlier forum regarding rolling an introduced question regarded ballast and material. As our 27' Marben was a 'Quick' roller that would about cast one off the boat if an unexpected movement was experienced. To the point that the purchase of the boat was under consideration. There were many qualified and interesting suggestions, stabilizers, rolling chocks, steadying sales and of course ballast.
We decided to go with ballast as stabilizers, rolling chocks and such didn't make too much sense for such a small craft. The end result was the installation of lead ingots 2" thick, 6" wide and approxamely 14 " long each weighing approximately 55#. these ingots totaling 825# were dispersed directly over the keel under the floorboards of the bilge area. What a total difference, speaking to the beam sea, where the boat use to 'snap' is now has a very gentile roll and the vessel raises up and down with the wave, not snap rolling. Head seas are now not a bow rearing rise but a soft slow rise reflecting the weight forward of amidships. Following seas have ceased being a wild turn to turn of the wheel.
So for our 27' overall 25' on the water with a 9.75 foot waterline beam, this addition of ballast has been the perfect solution.
Good discussion and there are lessons to be learned on the subject.
A.M.Johnson-Ketchikan (Bridge to Nowhere) Alaska

AusCan · Jul 27, 2013

Al - Yes, a good ballast certainly helps.
I have a powdered lead ballast in a sealed bulkhead down low in the center of the bow. Being sealed, it also provides extra safety if the hull is damaged hitting a reef.
I haven't seen powdered lead used in any other boats but it makes sense, as it fills the entire void and can be accessed via a sealed screw type inspection cover. There is no concern over the weight shifting in severe seas.

psneeld · Jul 27, 2013

brian eiland said:
So you agree with me that most any hull can be operated efficiently at displacement speeds. I was NOT asking about water skiing.

As far as the Shamrock hull shape is concerned I was suggesting that this hull shape might be expanded up to the ~40 foot size, and still be a reasonable hull configuration for a displacement operating trawler? Again I was not asking for a fast boat shape that your people are not wanting to wait for.

The Shamrock hull is basically just a slab sided Downeast (lobster boat) design. Nothing fancy or techie about it.

My point is that semi-displacement or the newer thinking semi-planning hulls are designed as a compromise....reasonably efficient at speeds up to near 20 knots and reasonably efficient at slower speeds...but really not efficient at either. If you never plan on going anything over hull speed then design it that way...not with a compromise hull shape.

Nomad Willy · Jul 27, 2013

I suspect the knotched chines as shown on post #152 is just to make a wide boat not so wide so it suffers less (efficiency wise) from it's wide beam.

Much can be done to control outwash and spray w similar chine shapes. A curved surface transverse to the flow of a fluid reduces it's velocity a lot.

brian eiland · Jul 28, 2013

Aku fishing vessel & Defever trawler

Marin said:
Well designed displacement hulls are easily driven which means you don't need gobs of power which you can't use anyway. Small-ish engines burn less fuel which means the typical single-engine Nordhavn has a great whacking range to it which is what you want if you're going to cross a big chunk of ocean.

And I don't believe there is a rule that says displacement hulls have to have round bottoms and chines. I've posted these shots before, which I did not take, but it shows one of the sampans or aku boats that were built locally in Hawaii in the later 1940s and early 50s for the tuna (aku) fishery there. These relatively narrow boats incorporated flat albeit curved bottom sections, hard chines, and even gunwale " hull bulges" (my term) to provide roll stability in the often very rough waters these boats fished in, like the infamous Molokai Channel. The "hull bulge" is obvious in the second shot and was quite effective as these boats were often rolled to their gunwales in the windy swells and waves around the islands.

But displacement boats they were, most of them powered by a single GMC 6-71. Watching them knife through the swells and waves like destroyers was a beautiful thing indeed. I filmed on a few of these boats in the 1970s and while they certainly rolled around-- hell, even sperm whales roll around in the Molokai Channel-- it was amazingly easy to keep one's balance and footing while on board. I have no idea who designed the hull-- all the aku boats had the same basic lines above and below the waterline-- but whoever it was, he understood the nature of the open ocean the boats were going to work in and how to design a hull to effectively meet the challenge.

The boats were almost exclusively crewed by Japanese Americans and I was told the word "sampan" is the Japanese term for carvel or smooth-sided planking, as opposed to lapstrake.

The bottom line being that a displacement hull does not automatically have to mean super-rolly.

I found these two hull shapes very interesting, and rather similar in form. The DeFever has the added feature of bilge keels.

Is this Defever hull shape unique to this particular size vessel in their line?

Nomad Willy · Jul 28, 2013

Is the boat in the pics really a DeFever?

Isn't it Ben's Eagle?

Whatever it is it's not unusual in any way that I can see other than the bilge keels.

It's a beautiful FD hull w a steep run aft that rises to the WL at the stern. All FD hulls have this feature or the equivalent such as a double end flat bottomed dory.

The hard chines increase stability very slightly and dampen roll very slightly and increase wetted surface very slightly so really play almost no part in the design overall.

The boat Marin posted is significantly unique in that she is very "pointy" in the bow and as a result carries very little of her displacement fwd. If she were a car you could say she had a short wheelbase. Also the stem is straight and extends all the way to her keel that is (I believe) also straight.

IslandEagle · Jul 28, 2013

brian eiland said:
I found these two hull shapes very interesting, and rather similar in form. The DeFever has the added feature of bilge keels.

Is this Defever hull shape unique to this particular size vessel in their line?

See my answer here: Trawler Forum - View Single Post - Hull Shapes----Show us your girl's bottom

Yes, in some ways the hull form of Island Eagle is similar to a sampan, although a sampan is much more stretched out.

If you are interested in hull forms and their effect on boats, I would highly recommend Gerr's The Nature Of Boats. You should be able to find it in most public libraries, or here: http://www.amazon.ca/The-Nature-Boats-Esoterica-Nautically/dp/007024233X

Scott Welch
Island Eagle

brian eiland · Jul 28, 2013

Marin said:
And I don't believe there is a rule that says displacement hulls have to have round bottoms and chines. I've posted these shots before, which I did not take, but it shows one of the sampans or aku boats that were built locally in Hawaii in the later 1940s and early 50s for the tuna (aku) fishery there. These relatively narrow boats incorporated flat albeit curved bottom sections, hard chines, and even gunwale " hull bulges" (my term) to provide roll stability in the often very rough waters these boats fished in, like the infamous Molokai Channel. The "hull bulge" is obvious in the second shot and was quite effective as these boats were often rolled to their gunwales in the windy swells and waves around the islands.

View attachment 12999

Hi Marin.
Can you define the 'hull bulge' portion of the vessel that you speak of?

Is it up near the gunwales, or that somewhat bulgy flat hard chine portion below the waterline?

bluebyu · Jul 28, 2013

Marin is retired, he only lurks here.

brian eiland · Aug 11, 2013

Roll damping on two New England trawlers: an experimental study

This reference was just brought up on another forum by a fellow from Australia

watto99 said:
In my own search for this information I tracked down a report and bought it on line for $40 from the US naval archiect association.
It's well worth the money and answers the questions about benefits and optimum design of bilge keels etc

Roll damping on two New England trawlers: an experimental study – C. A. Goudey, M. Venugopal – 1989, April.

An experimental study on three types of roll dumping devices – bilge keels, passive bilge fins, and paravanes is described. These tests were conducted in the MIT Ship Model Towing Tank using scale models of a 76-ft single-chine trawler and a 119-ft double-chine trawler. The models were fitted with each damping service and excited in roll by a hull-mounted moment generator. Roll motions were measured at zero speed and at trawling and steaming speeds.

Nondimensional damping ratios have been calculated and the effects on roll damping of each device are compared.

The relationship of bilge keel and bilge fin area as aspect ratio to damping ratio are studied and some design considerations are presented. Practical aspects of each device type are also discussed.

Ya mon · Aug 27, 2013

Art, I am looking into getting a 1985-1988 44' Tollycraft w/ twin diesels and I will be living aboard in St. Maarten full time with cruising the Carribean as a plan. I will be retired and I was wondering about your thoughts on a Tolly in this boating environment. Also, do you have any fuel burn or mileage estimates for the Cat, Volvo, or Detroit motors?
Thanks

Do trawlers roll a lot?

Guru

Guru

Guru

Guru

Attachments

Guru

Guru

Guru

Guru

Guru

Attachments

Guru

Guru

Guru

Guru

Guru

Guru

Attachments

Guru

Senior Member

Guru

Senior Member

Guru

Veteran Member

Similar threads