Semi-displacement and Full Displacement Hulls

Sailboats, the big U.

Rowboats have crossed the Atlantic so there is not need for a discussion that semi-displacement or planing boats are not qualified to cross big open water. The discussion of sail boats (almost all full displacement) is fairly on point in that few powerboats less than 60 feet have crossed an ocean. As the 2004 Nordhavn rally demonstrated we have a lot to learn about 24/7 operation of powerboats. Sailboat technology has had thousands of years to perfect.

An important point for me is that all boats are designed and built with a target market and target use in mind. The compromises are driven by those decisions. Speed or distance. Storage or living space. Hugh windows or windows which can take a hit. The list goes on and on. If you take a boat designed for one use and use it for another it may work for you, but some of the design elements may not be best for your use.

It is often said that if you can tell how you are going to use your boat you can narrow down the boats to look at.

Full displacement is geared to long distance cruising. Semi-displacement gives up some sea keeping ability for faster speed. Full displacement generally has more storage space. Both types of boats are fine.

psneeld said:

Asking what cruising boats are in Alaska is like asking what boats are in Key West, Norfolk and Newfoundland on the East coast.

Getting to Juneau could be almost any boat, getting to Homer takes a bit more...but not a whole lot more boat or much better captain.... and cruising to Attu Island or Nome would take yet another level of boat and or skill in my eyes.

Kevin can blast that if he wants...or hopefully see my point...but I know something about all of those waters from my travels on USCG Cutters and living and pleasure boating out of Kodiak for 2 years...plus the many rescue and fisheries missions I flew up there seeing what it was like on the water 365 days a year.

Just like any water...some people are only comfortable and even capable with certain types of boats while other are perfectly happy and safe circumnavigating inJWieboldt@homepowersystems.net bathtubs.

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I completely agree!

That is actually the point I'm trying to get accross!

Thanks!!!

Bay Pelican said:

Kevin

Whenever I discuss what is needed for a cruising boat to go to an area I ignore the purely local boats. Their needs are different. What percentage of the cruising boats coming up from the lower 48 states are planing versus full displacement?

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Actually Marty I've see several types of "new arrivals"

First are sail boats. They come here from everywhere.

Then there are the really large yachts. Boats over 70' with crew etc...

A couple Nordhavns come every year.

I've yet to see a KK although I'd love to!

Then there are the boats being brought up by new owners from the lower 48 states. Some number of these leave as well.

The point of my post was and remains that if XXX boat can ply the local waters it can cruise along any coastline. If a boat can make it to Seward Alaska it can go anywhere in the North and I beleive the central americas.

Crossing the gulf of Alaska is a minimum of 210NM of open ocean. I cannot think of anywhere in the north or central americas that is further with no place to escape bad weather.

There are GB's here. There are a variety of TT's here. There are Tollycrafts. There are are three of my model of Bayliner here. There's a nice looking Navigator as well.

Each and every boat here made it safely across the Gulf of Alaska. Each and every boat here leaves our harbor and they go cruising in the Gulf of Alaska.

Kevin - Flying over all that water was definitely a love /hate relationship...loved the scenery...hated the thought of ever having to ditch....

....almost hard to imagine cruising it and feeling completely relaxed due t the weather, water temp and the immense remoteness of it all....

....as I said...the run just up to Juneau seemed a cakewalk compared to pressing on.

Only up over the ice did it ever feel a little better...then you would think of all the white bears licking their lips....

markpierce said:

A flying bridge is fine for watching fireworks. Good thing Ray/Giggitoni has one.

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Phooey! The views were fine from the foredeck yesterday. See no use for a flying bridge now.

eyschulman said:

I think all the trawlers mentioned have their place and each type has probably multiple examples of successful long passages. However if you are talking the big U and we stick to pure sea keeping ability economy and crew comfort and safety the motor sailor or modern ocean crossing sail boat with a good auxiliary and fuel tankage has to be #1. As for speed most long range motor boats run 6-7 knots unless they are large. A good sailboat of equal WL can with wind and motor also average 6-7 K and roll stabilization is built into the design. The basic design of most open ocean rated sail boats is far superior to the typical high freeboard power boats being quoted for the big U transit. Until recently most long range cruising has been done with sailing or sail assisted boats. Beebe kind of helped push a revolution in ocean crossing motor boats. Nevertheless the sail boat is still there and in many ways with modern diesel motors still the ocean jumping champ.

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Good points. I have to agree.

Although many different boat types can handle short runs across unprotected blue water, motor sailers are perhaps the cheapest way to do it comfortably within a pilothouse.
I would guess that my local cruising waters are similar in roughness and in isolation, to the Alaskan waters. (although perhaps a bit warmer)
Finding a pilothouse boat that could handle these waters with some form of roll stabilization for under $50K, a motor sailer was my only option. If I had 10 X that to spend on a boat, I'd have plenty of choices.

Billylll said:

I don't need to be sold on the merits of an upper helm. I don't want one. What I'm asking would there be less roll due to having less weight and windage by removing the upper fiberglass?
What is the general consensus on the looks of the boat without the upper helm? I confirmed the picture photo shopped is a Mark I not a Mark II. The Mark II has no cockpit area only a full width and length aft cabin.

Bill

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Coming in on this a bit late Billy, and sorry if anyone else picked up on this, but strangely, being no great fan of the flybridge myself either, even though I have one, your comment re having no rear cockpit is the one thing which would make me hesitate if I had your boat. It is the only sit outside in place you have, seeing perched on top of an aft cabin is hardly the place to be, usually too narrow unless set out as a full width sub-deck. If you removed the bridge, and covered it with panels etc, then you are either in the boat or off the boat, there being no nice perch out on deck.

The cockpit is the top of the aft cabin, I should have made that more clear, then there is the bow area which while anchored is perfectly safe to use. The rear aft roof is surrounded by guard rails so it's not like it's a nothing or all situation.
Bill

Just want to throw something out to the OP and all others contemplating a long trip such as big U. What about the price and availability of fuel? With the present price and what's happening in the mid east I would strongly advise deep thought on fuel economy and the cost of funding the trip and we have not even had a oil crisis yet. If I were contemplating such a trip and had to watch my budget I would be looking toward sail assisted boats with great(not good great) fuel economy. Considering the lack of a definition of what a trawler is many could qualify maybe in the category as sail assisted trawler. I don't always follow my convictions by putting my money where my mouth is. In this case I have. I scooped up several hundred thou in Can and Us oil stocks over the last three years. I remember the last oil crisis and what happened to motor boat use and sales. I also remember how sail boats cruised through that crisis. This may not be a big issue for dock furniture boats or short distance use but it certainly would be a major big U consideration.

eyschulman said:

Just want to throw something out to the OP and all others contemplating a long trip such as big U. What about the price and availability of fuel? With the present price and what's happening in the mid east I would strongly advise deep thought on fuel economy and the cost of funding the trip and we have not even had a oil crisis yet. If I were contemplating such a trip and had to watch my budget I would be looking toward sail assisted boats with great(not good great) fuel economy. Considering the lack of a definition of what a trawler is many could qualify maybe in the category as sail assisted trawler. I don't always follow my convictions by putting my money where my mouth is. In this case I have. I scooped up several hundred thou in Can and Us oil stocks over the last three years. I remember the last oil crisis and what happened to motor boat use and sales. I also remember how sail boats cruised through that crisis. This may not be a big issue for dock furniture boats or short distance use but it certainly would be a major big U consideration.

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I doubt I'll actually get to do the complete big U. Realistically the pacific coast through Mexico is highly probable. I've already done the northern half, twice so I'm halfway there. The rest is a dream, but it'll take the Admrials blessing and we'll have to see where that goes.

When discussing the costs of long distance cruising we need to realize that the cost is spread out over time. Time measured in years for most of us. The realistic calculation of fuel costs is based on how much cruising vs how much exploring on land you plan to do.

Our cruising plans involve using the boat as a home base to explore from. I'm thinking we'll probably move the boat no more than once a week and only as far as the next port. I'm estimating worst case 100NM a week at 1.75NMPG or say max 60 gallons a week. extrapolating that into a monthly expense I anticipate around a thousand a month in fuel costs. This isn't a budget amount, its a guess as to what we'll be spending based on our preferred cruising style.

Some people might prefer to cruise more. They, depending on their budget requirements might need to consider a more fuel efficient boat, either by design or by size or both.

Marty wrote;
"Rowboats have crossed the Atlantic so there is not need for a discussion that semi-displacement or planing boats are not qualified to cross big open water."

Any rowboat that would cross the Atlantic will be beyond any doubt a FD boat. And for that matter any rowboat that's actually a rowboat will be FD. Any boat designed to row must be efficient enough to get along well with just human power. Usually only one or two humans. With that small amount of power only FD boats need apply.

I exclude multi-purpose boats that are sometimes or even fairly often rowed like an aluminum skiff ... But they are not rowboats.

Actually the only need for something other than a FD hull is the need for speed and that usually isn't a "need". Most trawlers would be better off if they all were FD.

manyboats said:

Most trawlers would be better off if they all were FD.

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Now yer just trolling for arguments...

That's like saying we would be better off if we all lived in Florida......Well, no, it would be different, but not necessarily better. Or we should all drive Volkswagen Beatles because it would save fuel.....actually that's a good idea, smart cars for all.......

Full Displacement hulls are fine (that's a pun), but they have drawbacks, lack of dynamic stability, high resistance at speed, lack of interior space, and lack of at rest stability (high roll angle).

Semi-displacement hulls have drawbacks as well, high resistance at low speed, quick motion in a sea, some may have a shallow forefoot that will pound going uphill, and they may handle poorly when forced to slow in a really big sea.

I'm just thankful not everyone wants to chug around in the same boat.

Tad Roberts said:

Now yer just trolling for arguments...

That's like saying we would be better off if we all lived in Florida......Well, no, it would be different, but not necessarily better. Or we should all drive Volkswagen Beatles because it would save fuel.....actually that's a good idea, smart cars for all.......

Full Displacement hulls are fine (that's a pun), but they have drawbacks, lack of dynamic stability, high resistance at speed, lack of interior space, and lack of at rest stability (high roll angle).

Semi-displacement hulls have drawbacks as well, high resistance at low speed, quick motion in a sea, some may have a shallow forefoot that will pound going uphill, and they may handle poorly when forced to slow in a really big sea.

I'm just thankful not everyone wants to chug around in the same boat.

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Well, soon he'll be back to telling us how little horsepower we should have and what idiots we are to have more. I'm sure he'd hate our boats but that doesn't bother me. I am a bit bothered in making absolute declarations as fact that are simply opinions. "Most trawlers would be better off if they all were FD" confused me between "most" and "all" but it's a statement that he simply can't make. No one can state what another person would be better off with.

My wife and I have our preferences in boats but we don't ever try to present our choices as being the "right" ones and "only right" ones. We do try to discuss all the options and encourage people to choose for themselves. In fact, not once here have I ever mentioned or suggested any brand boat we own. But the fact is there are many very happy persons who own semi-displacement and even planing boats and use them for the same type cruising as FD, just faster and at a little greater cost. Similarly there are many who have no desire to go more than 7 knots and love their full displacement.

I'm very glad there are different boats for different people and that we don't all want the same. Wouldn't that be boring?

manyboats said:

Actually the only need for something other than a FD hull is the need for speed and that usually isn't a "need". Most trawlers would be better off if they all were FD.

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Oh Eric, I guess its sunday, and its raining, so I'll take the bait

I'll argue that if you separate "passagemaker trawlers" from "Coastal Cruiser trawlers" then most "Coastal Cruiser trawlers" would be better off as SD boats. I'lll also argue that the VAST majority of "trawlers" designed for coastal cruising are in fact SD boats already and for good reason.

For Coastal Cruising SD boats have several key advantages...

1. Speed and power. Afternoon "sea breeze" is a widely recognized effect in coastal areas. The speed of a SD boat can get you to the next port in calmer weather, avoiding the rough sea states typical of afternoons in coastal areas. That is just one example of many I can think of where speed and power have an advantage.

2. Stability at anchor. A SD boat with its higher initial stability rolls much less at anchor or in harbors that experience surge.

3. View and visibility. Although not a hull form specific issue, most SD boats have larger windows, offering greater visibility.

4. Larger interior living space. I know most won't believe this but its true. Compare living spaces on MOST SD boats vs MOST FD boats of the same design type, and you'll find more interior room. This isn't always the case, but it is what I've personally observed, and its the very reason why I have a Bayliner 4788. For those that say interior space doesn't mean much, try it some time. Larger interior spaces equals more comfort.

The ONLY thing that makes a FD boat better than a SD boat for coastal cruising is sea keeping ability. I will admit that a proper FD boat will be more comfortable in larger seas. This is mitigated though by the "why leave the harbor" concept. If its rough out there stay put. Enjoy the place you are at. Relax, explore another day or two. The weather will change.

For those that think the seakeeping ability of a typical FD boat is necessary, I'll counter that its all about perception and roll tolerance. Last weekend I was in a bouy measured 6.2' 10/7 second beam sea and used my boats large engines to squat the rear into a very enjoyable ride. I would argue that in moderate sea states a stabilized FD and a stabilized SD boat can both be comfortable. Take the stabilizers away from both boats and I've yet to see data that a SD boat is any less comfortable, if it uses its engines to dampen the sharpness of the roll.


Let the fur fly.

For once I'll agree with the QBBL guru....but only if we narrow down the definition of a trawler.

IF...you think a trawler is something just like what manyboats has in HIS mind...OF COURSE they are all better off being FD....

We all know that trawlers are this magical, workboat look alike with highly glossed varnish jobs,

plus a 45hp, 1890's designed engine that turns max 87.3 RPM and pushed along at 5.2361 knots because no one should go faster...

and don't forget a QBBL that a rollercoaster addict could relate to...all with unlimited storage and range, yet can fit into tiny marinas for a song in dockage, carry 30 anchors and a few spares (easy as there's no genset so there's plenty of room below...there's no genset because trawler owners are green and noise conscious)....

I'd go on but that ought to do for now....

psneeld said:

for once i'll agree with the qbbl guru....but only if we narrow down the definition of a trawler.

If...you think a trawler is something just like what manyboats has in his mind...of course they are all better off being fd....:d

we all know that trawlers are this magical, workboat look alike with highly glossed varnish jobs,

plus a 45hp, 1890's designed engine that turns max 87.3 rpm and pushed along at 5.2361 knots because no one should go faster...

And don't forget a qbbl that a rollercoaster addict could relate to...all with unlimited storage and range, yet can fit into tiny marinas for a song in dockage, carry 30 anchors and a few spares (easy as there's no genset so there's plenty of room below...there's no genset because trawler owners are green and noise conscious)....

I'd go on but that ought to do for now....

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???

psneeld said:

For once I'll agree with the QBBL guru....but only if we narrow down the definition of a trawler.

IF...you think a trawler is something just like what manyboats has in HIS mind...OF COURSE they are all better off being FD....:

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Exactly what I thought, and given his clear expressions in many other threads, the statement makes total sense about vessels whose design was never intended for speed. Performance is a different thread.

One things is for certain...a quote right out of Alice in Wonderland makes a point that is totally relevant to the discussion...

"Sometimes I believe in as many as six impossible things before breakfast.”
—Alice, Tim Burton’s Alice in Wonderland

If you keep shifting a reference point...everything you post will make sense...some are masters at it....

Another universal axiom is "clarity of thought"....I have sat in audiences of some of the finest minds in our known universe....I have also sat on a barstool next to some of the universes biggest drunks....the "clarity of thought" emanating from either source seemed to be "clear" at the moment. The next day...it was a heck of a lot more evident who was speaking something I could agree with.