Trawler Design and Performance Parameters

[fdw]

I'm making the transition from sailboats to trawlers. From my sailing days I know there are parameters used to describe a sailboats design and performance: displacement / waterline length; ballast / displacement; comfort ratio; capsize screening rating; PERF speed rating; and probably more.

Are there parameters typically used to describe trawler design and performance?

[DavidM]

Most of those parameters are available for trawlers as well and I can’t think of any additional relevant parameters specifically for trawlers. A hull is a hull whether it is a sailboat or trawler.

Of course most trawlers do not have the full displacement hull shape that sailboats do. Also capsize parameters aren’t so important for trawlers given that 99% don’t operate in conditions that warrant consideration of those. Maybe that is also true of sailboats as well but their inherent need for stability makes it easy to consider those parameters.

David

[Jeff F]

The big variable is design speed. An awful lot of other decisions flow from that.

[ddw36]

I suggest you read Robert Beebe's Voyaning Under Power, available at Amazon. He spends considerable time discussing hull designs for trawlers.

[mvweebles]

Originally Posted by fdw

I'm making the transition from sailboats to trawlers. From my sailing days I know there are parameters used to describe a sailboats design and performance: displacement / waterline length; ballast / displacement; comfort ratio; capsize screening rating; PERF speed rating; and probably more.

Are there parameters typically used to describe trawler design and performance?

I'm hoping Hippocampus will chime in - he was very transparent with his transition from offshore sailing to trawlers and is quite the hobbyist architect.

Suggestion to read Beebe's "Voyaging Under Power" is a good one - it's the bible for old-school trawlers. Another good read is George Beuhler's Troller Yacht book.

In the end, it really depends on what you want to do with the boat. If your ambition is some flavor of coastal passaemaking, meaning 2-3 days, speed (including design speed, which is influenced by what is called Prismatic Coefficient), range, and weather tolerance (metrics include AVS - Angle of Vanishing Stability; and A/B Ratio - above/below waterline profile) are important. If goal is to do The Great Loop, then air draft and comfortable beds are important.

Bottom line - if you can provide a bit more context, the answers will correspond.

FYI - I'd guess that somewhere around half of the active TF contributors are recovering sailors. You're in good company

Peter

[fdw]

Thanks all. I have just ordered Beebe!

Here's an example of a database used by sailors that presents sailboat design and performance parameters:

https://sailboatdata.com/sailboat/cape-dory-36

Is there an analogous data base for recreational trawlers and motor yachts?

Thanks.

[Choices]

If your doing it for armchair research then knock yourself out.

But after touring a dozen boats you will figure what you want.

Big difference in build quality, looks, seaworthiness, and cost/ resale.

For us a long passage is 24-36 hours, non-stop. Usually 8-10 hours is all the crew can stand. They go stir crazy.

While lots dream of long cruises into the sunset very few go more than twenty miles from land.

Best advice, be very realistic on what your going to use the boat for.

[mvweebles]

There is not much comparable to sailboatdata.com; maybe McKnew's Powerboat Guide that lists production boats with some commentary. Useful for floorplans.

I think the key difference is sailboats of all types are routinely raced - even beer can races. So there are ratings to adjust for different hulls and the criteria are well known. Over the decades, sailboat design was heavily influenced to eek-out the most within the confines of race design limitations.

In short, sailboat design has generally sought to define objective design criteria. That does not really exist for powerboats beyond displacement vs semi-displacement vs planing hulls; and horsepower ratings. There used to be discussions on deadrise (angle of the flat aft hull sections - a deep-vee is more difficult to plane, but rides better in chop), bow sections/flare, etc. But these are rare and more interesting to explain than to forecast. There are few true displacement boats out there, and most folks want some flavor of semi-displacement with the premise that they'd like a turn of speed to outrun weather or catch a bridge opening. Tradeoff is economy, of course.

Powerboat design is much more influenced by intended usage, perhaps budget. The classic aft-cabin motoryacht or sundeck trawler style has the most interior living accomodations, but is not a good platform for fishing or if there are any mobility issues (incuding having a large dog aboard). For those with regular full-time jobs and defined vacation periods, tradeoff for speed vs economy is easy - a 15-kt boat has a maximum cruising area of about 175 sq miles vs a 7.5-kt boat's 45 sq mile max. That's a big difference for a long weekend.

If the intended usage is cruising to distant destinations across open water, the variability of weather will drive certain attributes. For example, for many, stabilizers are strongly prefered by many. Or higher bow sections. Or whether or not you want/need a generator. Bow thruster, etc. Much of these choices are now part of sailboat selection too.

I hope this helps - it really comes down to usage and budget. Not too dissimilar to sailboats, but the criteria are a bit more subjective.

Peter

[Hippocampus]

Manufacturers are pretty opaque as compared to sail. Even for voyaging power simple numbers like AVS or a Gz curve are nearly impossible to get. As you know there’s considerable back and forth if a comfort quotient is a valuable number to consider but just try getting one from the builder. It’s unlikely. It was very disappointing trying to get reliable statistics for small power cruisers. Think in part because the general public doesn’t demand them and in part because rallies and races don’t occur often with power. Commonly for joining ocean rallies you need to have a boat that meets certain criteria and of course since unfortunate events in races not only are performance statistics required but also safety.

There are major differences in how power and sail handle adverse weather but also in downflooding risks. Although on occasion sail will use an engine to mitigate risks in weather the concern about failure of propulsion is and viewed differently. Nature and placement of ducting for engine room air intake (and exhaust) is of major concern for power. Also downflooding risks from breaching of windows and doors is amplified in small trawlers given the larger size of glass and the absence of traditional companionways.

Mounting of heavy structures is also not usually given the attention paid to in sail. Simple things like locking floorboards or bonding mounting of household appliances (freezers/ refrigerators etc.) or really secure closures of lockers commonly doesn’t occur. Whereas there’s a reasonable expectation an ocean rated sailboat will survive a knockdown, come back up quickly and continue to function this is not the case for many small recreational trawlers.

I did get stability information from diesel duck but it uses a Chinese system I’m totally unfamiliar with so basically uninterpretable to me. N and KK gave me language but not the hard numbers I sought. Particularly a Gz curve. Both have excellent reputations as sea boats but it’s hard to do a side by side comparison.

Buying the current boat we looked at DD46, N43 and KK 42. Eventually wife said she was done with voyaging and wanted coastal. Looked at various brands but knew we’d do some near shore as well as coastal so narrowed things down to AT, NT and helmsman. Helmsman was gorgeous but I thought (possibly incorrectly) she would be more expensive to run and not as good a boat near shore. Both the AT and NT seemed well constructed with the NT being narrower and with less room as a result. However I thought the NT would be less expensive to run and possibly better near shore. I don’t know if any of the above is true. It only my impression.

When shopping I was struck by the large variance in construction details between trawlers of similar size. Also the amount of wasted space and relative lack of storage compared to similar sized sailboats. That large salon with its big windows is wonderful at anchor but difficult to make safe in a seaway. I needed to go through a change in gestalt. Except for a very few recreational small power are not designed for voyaging in mind. The concessions required and the extreme increase in costs of construction are not justified for the common use pattern of most recreational boats. That being the case the numbers you and I are looking for don’t rise to the same level of importance. Hence they aren’t part of the marketing program of manufacturers.

I still look at the N43 and N47 with envy until the wife points out the many days we’ve kept the NT42 at 10kts for the whole day or went WOT to avoid a close crossing. We’re now a year into a SD boat. In no respects is your thinking, planning or use pattern the same as with a passage making sailboat. As difficult as it is don’t try to equate them.

[dannc]

In the EU, there is the RCD CE rating, https://www.imci.org/63.

What is category?

There are four Categories: A, B, C and D. They classify both maximum wind speed and maximum significant wave height for which a product is designed.

There is also the STIX rating which is an international rating for boat stability.

For EU boats, the Category should be available, but getting the STIX number might be more of a challenge.

Later,
Dan

[Comodave]

What type of cruising do you plan on doing? If you are going to cross oceans then maybe all the esoteric numbers may be useful. But if you are going to do coastal cruising or the loop, then look at layout, condition of the boat, and what meets your needs. Getting the ultimate in fuel economy or performance aren’t that important unless you plan on crossing oceans. Good luck in your search.

[Hippocampus]

Problem with the EU system is it’s a statement as to the capabilities at time of initial launch. And only at initial launch.

Depending upon components used, design and execution of construction how long the vessel is really capable at the initial designation may vary widely. Knowing if the vessel was built to ABYC, Lloyd’s, Veritas or other class criteria may help in judging long term durability but a EU classification tells you little about construction details that may come up during your time of ownership imho. STIX maybe more meaningful but again doesn’t address durability.

So you can be on a boat with the same rating as another boat and the two be no where close to each other as to capabilities or behavior in a seaway.

[FWT]

No, as others have said, there appears to be no such online resource that catalogs makes, models, and characteristics.

There is no substitute for the "shoe leather" approach. Hard work. There are a couple of places to begin. Yachtworld for listings of boats, which has both new and used. You can go to the websites for the big boat shows like Ft Lauderdale and go to the lists of boats shown there, and systematically look up anything that has a shot of being what you want. Go through the online magazines with promo articles, where even the ads can be your friend. Walk the docks and yards to see if there is anything interesting that you can later look up. Talk to a good broker if you can find one.

Folks here are knowledgeable. So if you find something that is somewhere in your ballpark, a question that involves "something like a 'SuperTrawler 50', but older / younger and having more of this and less of that" should yield suggestions. At the moment we don't know much about your ballpark.

Its time consuming hard work, but sadly there is no substitute. There is no magic.

[ranger58sb]

We started from the other direction. What features did we need/want/not want, etc. Things we'd "interface" with ourselves. Like the galley. The master stateroom. The head. The bridge (including stairs, not a ladder). Transom door. Swim platform. Aft-mounted helm on the bridge. Et cetera.

(Hulls are there, but we don't personally do much direct "interfacing" with them.)

Then we evaluated the TWO boats that passed all of our requirements. Well one did, anyway, a second came close. (No kidding, out of the bazillions of brands and models we reviewed.)

THEN we paid attention to engines, hull design and construction...

And decided it was all OK, bought the one.

All that might have been different if we were buying a NEW boat... or if reams of boats had met our initial criteria.

But new is beyond our budget given all those "interface" features. And with only 1 (or 2) candidates to consider... our budgeted approach pretty much made all those minor hull shape details... almost beside the point.

Also might have been different if we were planning ocean passages. Not. Royal Clipper is our idea of an ocean passage.

We've seen similar questions about engines. Which brand, model, etc is "best" -- or at least better or preferable -- but in the grand scheme of things, if the boat is selected based on user "interface" criteria, you get to the point where you may or may not have any choice in engine(s) -- or at least very limited choice -- depending on the marketplace at any given time.

Just thoughts...

-Chris

[Hippocampus]

Chris unfortunately I agree with you. It’s not because people on motor are less knowledgeable nor have shallower pockets but the culture is different. Think it stems from how new boats are sold. Usually cruisers will want to know is it stick built or glued, details of the layup, bulkheads fully glassed in or just tabbed, brand of through hulls/hoses and all the little details of construction. Yes some people buying power are just as compulsive and an a lot even more than the average sailboater. But when shopping got “well was never asked that.” more often than when shopping for sail. Think that overflows in asking for or researching for the usual statistics that are available for sail. You can get the best survey there is and vet as many boats as you want but that doesn’t tell you AVS or substitute for a Gz curve. Rather need to change your mindset. Most recreational boats (and that includes sail) don’t voyage. Those numbers have little importance for most people. They do become relevant to those people who are voyaging in power or offshore cruising. Here you’re betting your life on your boat. So not only are the numbers important but also nature of construction.
A blue water boat isn’t just the numbers. The NT has very nice pilot house doors but nothing like the strength of the N. Nauticat makes very stout strong motorsailors. But they are B not A because the pilot house doors slide. It’s lovely that the salon windows slid open and have integral bug screens. Stronger and less likely to leak in a seaway with them being fixed and over built. Sailboats (at virtually all price points) come with ocean rated hatches, port lights and companion ways designed to take a pooping.it’s like comparing a HD 2500 dually to a sports car until you get into powercraft designed from blank paper to be blue water.
Best of luck on your search . First decision is how you are actually going to use the boat. After that the choices are markily decreased.

[rslifkin]

There are definitely some details of my boat that are unknown to me. Like AVS. But I haven't worried about that, as there are obvious points of concern around downflooding, etc. that would become a problem before AVS was limiting. And being that a powerboat isn't susceptible to the kind of wind-induced knockdown a sailboat is, it's easier to avoid situations that might test the AVS limits of the boat.

Some features are also made less necessary by not so obvious other features. Some powerboats truly aren't watertight enough, but at the same time, for a typical flat transom powerboat, pooping is a far less likely situation than for many sailboats. Particularly if the powerboat can exceed hull speed. The wide stern gives a lot more buoyancy, making it harder for a wave to end up on top of (rather than under) the boat. And for boats where increasing speed (even if just briefly) is an option, you gain more options for active tactics to handle an ugly wave approaching your stern. An average powerboat often has more freeboard than a similar size sailboat as well (although modern sailboat designs have gotten taller), so there's even more reserve buoyancy available there.

There's also a big difference in how the boats feel between power and sail, especially for lighter weight powerboats. On many powerboats, the ride will have you screaming "I'm never trying that again!" long before you're actually testing the boat's limits.

[dannc]

Originally Posted by Hippocampus

Problem with the EU system is it’s a statement as to the capabilities at time of initial launch. And only at initial launch.
...

Yes but that is no different than some of the other metrics that are used. Understanding the "numbers" is critical so one knows how to weigh them. The EU has a system which answers the OP question. Are the EU ratings perfect and an end all? Of course not.

But it is one more piece of data, if available, that might be useful.

There are boat building methods that will make me stay away from some boats yet those boats have good "numbers."

Later,
Dan

[Hippocampus]

Pooping-RS all good points however dependent upon the props spinning. Most trawler designs will have the bow fall off the wind. Rather rapidly in a stiff wind and within the time to switch racors, clear fishing nets or deal with whatever caused the props to stop spinning. Whereas I felt totally secure in prior sailboats knowing I could throw a JSD over the stern even if I lost the stick I don’t have that sense in my current power boat. We do have a sea anchor on the NT but it’s a laborious job to set it up. Rather simply have avoided settings where seas are that large. Yes she’s a good sea boat but that depends upon everything working.
Dan agree but think it’s important for folks to understand the limitations of the EU system.

[mvweebles]

Originally Posted by Hippocampus

Pooping-RS all good points however dependent upon the props spinning. Most trawler designs will have the bow fall off the wind. Rather rapidly in a stiff wind and within the time to switch racors, clear fishing nets or deal with whatever caused the props to stop spinning. Whereas I felt totally secure in prior sailboats knowing I could throw a JSD over the stern even if I lost the stick I don’t have that sense in my current power boat. We do have a sea anchor on the NT but it’s a laborious job to set it up. Rather simply have avoided settings where seas are that large. Yes she’s a good sea boat but that depends upon everything working.
Dan agree but think it’s important for folks to understand the limitations of the EU system.

Curious if you ever deployed your Jordan Series Drogue (JSD), and if so, how was retrieval? What about the sea-anchor? I've never used either, never needed one, but you have a much more mid-ocean experience than I ever will. By all accounts, full-blown parachute sea-anchors are a bitch to retrieve.

As mentioned in other threads, I just recently purchased a Burke Seabrake (HERE - <$300USD delivered). drift anchor. It appears to be very usable though it is not really sized nor designed for storm conditions though it could only help if only a bit. For a single engine boat such as mine (and your Nordic Tug), at least when venturing coastal, my thinking is I need to buy-time to make repairs and keep the boat from going beam-to seas, it's natural orientation. Also to abate drift.

Sidenote to the OP - exchanges like these about offshore tactics on a powerboat seem to be the domain of Hippocampus and myself. Few trawler owners concern themselves with such. Says more about the likes of Hippocampos and me than trawler owners as a whole.

Peter

[ranger58sb]

Originally Posted by Hippocampus

Chris unfortunately I agree with you. It’s not because people on motor are less knowledgeable nor have shallower pockets but the culture is different.

Usually cruisers will want to know is it stick built or glued, details of the layup, bulkheads fully glassed in or just tabbed, brand of through hulls/hoses and all the little details of construction.

Well, I guess I got a little carried away with my description, and maybe made it sound more overly-cavalier than it actually was.

I did indeed pay close attention to construction. Solid glass bottom, cored sides, tabs and joints, stringers, deadrise, etc. And both of our final two candidates passed all that.

I just meant that none of that came first. First, we looked for features that would make the boat usable for our purposes in our situation. That eliminated most (all but two) boats from almost the whole universe of boats -- at least within our (reasonably generous) used-boat budget range.

But then yes, once we got the list down to only a couple choices, I really did begin paying more attention to naval stuff.

There were actually about 15 other boats that came close but failed on one or two of the "I really want this" or "I really prefer that" criteria. I didn't inspect their construction much, since they had failed already. Saved lots of time, there.

-Chris