Cruising speed...

[Nomad Willy]

I agree. I would like to have a boat that was efficient at 7 knots yet be able to run at 15-20 knots when I wanted. I could have even bought a boat that could do that. However, since there are always trade offs, I decided that the ability to go faster wasn't worth the trade off for me.

I think I understand what Nomad is saying. If I wanted to always run at 10 knots, my boat would likely be the "wrong" boat choice. However, the PO says he ran the boat that way all the time. My boat just isn't efficient at that speed. Likewise, if I never wanted to run above 7 knots (I mean NEVER), then I also would have bought the "wrong" boat because the boat is way overpowered for that speed and the hull isn't as efficient as a FD hull of the appropriate LWL.

If I was always going to have 3 couples on board, my boat may be the "wrong" boat. If I were to only very occasionally have 3 couples on board, my boat is just fine. If we were never going to have guests on board, my boat would be overkill for its use, therefore the "wrong" boat.

Having the "wrong" boat for a given application doesn't mean someone made a bad choice or should have picked a different boat. We buy what we like and we use it as we wish and there is nothing "wrong" about that. However, it is probably a good thing, particularly for a new potential buyer like the OP, to carefully consider how they want to use the boat before they buy one.

Northern Spy has it right. A boat's operating envelop should cover everything you need/want and comfortably cover what you use the most. So if I want to be able to cruise between 6-10 knots but spend most of the time between 6.5-8 kts, the my boat is a good choice. If I wanted 6-10 kts but want to spend most of the time at 10 kts, my boat's operating envelop covers that, just not as well as another boat choice would have been.

The best speed for a boat is not about owners or captains. It's about hull design and power. Through ownership the boat operators can do what ever they want. But ownership dos'nt make what they do right or correct. The only ones truly capable of calling out operational speed ranges are the designers. Actually I ca'nt remember any of them doing it though.

So we've got a speed and power freak and somebody that has a speed connection w toasters. Spy we actually have two. Chris is gluten free and dos'nt want my evil bread in her toaster.

 

[psneeld]

There is a reason why you can't remember any of them making a big deal out of it......

 

[eyschulman]

Semi-displacement boats usually have smaller rudders.

And some have two motors. That should really get the purists going. Here is one to really upend the efficiency crowd. Two boats of equal LOA same motors and props. One classic FD design with overhangs and relatively heavy weight Vs a light same LOA thin SD with longer waterline(less overhangs). Which is going to be the more efficient. Absolutely not necessary to have a FD boat for efficient fuel burn. Yes there are other reasons .

 

[markpierce]

And some have two motors. That should really get the purists going. Here is one to really upend the efficiency crowd. Two boats of equal LOA same motors and props. One classic FD design with overhangs and relatively heavy weight Vs a light same LOA thin SD with longer waterline(less overhangs). Which is going to be the more efficient. Absolutely not necessary to have a FD boat for efficient fuel burn. Yes there are other reasons .

What? The majority of boat owners here have twin engines. That's what the demand was and builders responded. Or was it the other way around?

 

[BruceK]

So you DO have four toasters.
I knew it.

[emoji3]

The disconnect on the thread, and the "4" made me post this:

. It`s long so stop whenever you like, I just posted it for the four candles sketch.

 

[eyschulman]

What? The majority of boat owners here have twin engines. That's what the demand was and builders responded. Or was it the other way around?

There might be an element of the other way around. Many here for purposes of having a mobile cottage on the water have Trawler types(whatever that is) and that type of design particularly if FD lends itself to one main engine on design and installation basis. It is just a lot cheaper and easier to plop a single engine in a midline location.

 

[BandB]

The best speed for a boat is not about owners or captains. It's about hull design and power. Through ownership the boat operators can do what ever they want. But ownership dos'nt make what they do right or correct. The only ones truly capable of calling out operational speed ranges are the designers. Actually I ca'nt remember any of them doing it though.

.

Taking up where my wife left off, the purpose of boats and boating isn't for the designers. The judge of best isn't the designer. It's the consumer. It's the one who pays for it. If I buy one then I get to stay what I think about it. The best speed is the one that makes me, the buyer and owner happy. Designers design boats to appeal to the buyer and to be put to various and sundry uses and be driven whatever speed the buyer chooses within the capability of the boat.

The quality of any product is never determined by it's design or it's manufacturing but how it performs and how it is perceived by the consumer. Left to their own devices, engineers, much like you, would manufacture products that technically were sound but that no one would purchase. I've heard engineers many times over the years argue that something was stupid but if it was what the consumer wanted and it sold, it was never stupid. There is hardly any product out there that can't be made better. I've taken many of those better ideas before focus groups and seen them fail. Perceived quality is what sells and the purpose of manufacturing or building is to sell.

 

[Art]

Wow - This whole thang bout boat speed, hull designs, NA's, marketing, fuel use... etc... etc has gotten screwey!


My recommendation to the OP of this thread:


Find a boat that turns you on while at the dock. Then go for sea trial and if that turns you on too. Then have it well surveyed. If all three turn you on so much you start to get a ting in yer thing - if you get my drift! THEN, for Heaven sake - BUY IT!


Then - Go enjoy it!

 

[Nomad Willy]

If you want the last word ... you got it.

 

[markpierce]

Six knots are usually fast enough for me.

 

[Bay Pelican]

Tradeoffs, everything on a boat is a compromise. We have talked about speed and efficiency. However, seakeeping is also a factor in the boat's ability to go fast.

We have just completed a short passage between Martinique and St. Lucia. After 2 or 3 weeks of rough weather we had a weather window of only 5 foot seas on the beam. Most boats we know were on the move taking advantage of the one day opportunity.

The post passage discussions the night of the passage tell a lot about the tradeoffs between speed and seakeeping ability. The fast boats complained of rough weather and being bounced around, my wife and I joked about how it was flat and like being on a railway. I even commented that I was able to drink from a glass (without spilling) as opposed to a bottle with a cap on it.

We all differ on how we value the tradeoffs, but there are tradeoffs.

 

[Group9]

Our boat, an older Bertram 42 motor yacht, only has a hull speed of around 8 knots or so. But the sweet spot, fuel wise, seems to be about 6.5 to 7.5 knots. Running it up to ten knots, you really pay a lot in fuel to get those last couple of knots.

But, in a pinch, if necessary, it will do 15 knots WOT and will do 12 knots all day. But, you are going to pay for that speed, oh so dearly, in fuel. But, 99 per cent of the time, it is simply unnecessary to go that fast.

We like to think of our boat as basically being a 7.5 knot max trawler that can double it's speed in an emergency, or to handle seas or to avoid really bad weather.

But, being former sailors, a steady 7.5 knots feels like a hundred miles a hour to us!

 

[Art]

Our boat, an older Bertram 42 motor yacht, only has a hull speed of around 8 knots or so. But the sweet spot, fuel wise, seems to be about 6.5 to 7.5 knots. Running it up to ten knots, you really pay a lot in fuel to get those last couple of knots.

But, in a pinch, if necessary, it will do 15 knots WOT and will do 12 knots all day. But, you are going to pay for that speed, oh so dearly, in fuel. But, 99 per cent of the time, it is simply unnecessary to go that fast.

We like to think of our boat as basically being a 7.5 knot max trawler that can double it's speed in an emergency, or to handle seas or to avoid really bad weather.

But, being former sailors, a steady 7.5 knots feels like a hundred miles a hour to us!

Well put... and nice boat! I've always had a soft spot for Bertrams.

 

[eyschulman]

This is so increadible...semi-displacement boats in the right configuration are exactly the "versitile boat" that someone might think is the "wrong" boat.

Their concept is to be able to run fast when lightly loaded or when appropriate...and still be a decent boat at displacement speeds.....or really any speed in between.

A good example is a working boat like a lobster boat. It runs and guns as long as it can so the day doesn't last forever, as it fills with catch or pots, it may slow, but throughout its range it isn't killing the operator on fuel costs like a true planing hull would. A displacement only boat wouldn't work either.

The same principles might apply for a cruiser too.

So yes....a displacement boat can only do one tiny speed range...but a semi-displacement has quite a bit of speed range that the designer DID think about...and there are those with planing boats that know if they do slow to a displacement like speed, their boat isn't all that ineffecient.

Maybe that feature isn't a specific design feature...but both the designer and operators know it's there if they want it.

Right on. That is why my custom one-off boat after long years of boating on over 20 different boats including several FD SD and multi hulls is a SD with a down east hull. I have a sea kindly boat with a sliding speed range with the option of relative economy when below the hull speed of 9.2K and the ability to run all day at any speed up to and including 20K at max of 80% engine load. The lobster boat of which I have owned one was in my thoughts when I conceived and designed Moon River. Sam Devlin rounded out my rough edges artistically and technically to come up with the end product. Moon River will not find high marks among the Trawler crowd it is not nearly enough cottage for its size a endemic problem with lobster boats in general. This type of boat puts emphasis on the boat side of the curve and less on being at home on the water. Having lived on a Rec. Trawler a Pilgrim 40 in the past I fully understand and appreciate what is involved with the cottage on the water. The Pilgrim was used on the East coast in waters it was well suited for. Now living in the PNW where I transit rapids and regularly deal with remote areas a different kind of boat suits my needs in my golden years. Just a few years ago we were plying those waters with a 44 foot all out ocean racer a J/44, but things change. Now we need more protection from the elements less hassle with huge sails and the complexity of timing the rapids in a 7K boat, thus the DE SD power boat.

 

[psneeld]

Blows my mind how many people who claim experience, seem to miss what is right in front of them....

 

[RBack]

Generally speaking an SD hull is a hybrid.
Generally speaking hybrids are best at being [half] good at several different things.
Generally speaking they (hybrids) will be outmatched by the (various) specialists of each and every category (task) the hybrid can "compete" in.
Generally speaking the hybrid can strike back when it comes to tasks where the individual specialist is no specialist.
Generally speaking the hybrid is a specialist in being a hybrid, thus rather versatile - as already mentioned several times.

In biology it's almost equal to opportunistic organisms (crows, rats, etc.) versus highly specialistic adapted ones (peregrine falcon, anteater, etc.).
And I'm certainly not putting different values to peregrine falcons and crows here.
So don't misinterpret if you happen to own the crow (or rat) trawler.
Your boat will do just fine where/when the peregrine boat fails completely.

... generally speaking.

 

[Ski in NC]

I should have named my boat "Crow".

My jon boat IS named "Squirrel". And my truck named "Mule".

Just trying to stay on topic...

 

[Art]

We named our boat exactly what it is "The Office". Any time when people ask where we're going who we do not want along nor to bother us we simply say "... we're going to the office." Works every time. Even if they say but wait can't we discuss items. Our reply "... sorry we're already quite late in getting to the office!" "Maybe we can discuss in near future."

BTW - There is a lot of background in our Boat's name artistic painting.

 

[Nomad Willy]

Art,
I have a friend that calls Starbucks "the office".
An interesting friend.

RBack,
Great analogy but a true SD hull does supremely well at something planing and FD hulls do poorly at. That is running at speeds inbetween planing and less than wavelength speeds. A PU truck and a car do very well at what they do but those half cars half pickups things do'nt do anything well. Same w a motorsailer. Or a hybrid car. But at the speed she's designed for SD hulls are wonderful doing the mid speed thing and what's they are designed to do .... well at. It's not that they ca'nt do anything well. They do the midspeed thing very well.
You wrote;
"Generally speaking the hybrid is a specialist in being a hybrid, thus rather versatile - as already mentioned several times."
Not very versatile at doing very well (higher speeds and lower speeds) but very well at in-between speeds. Can't go high at all and does poorly at low. Does only well at SD. All three only do well at what the're designed for. But the planing hull is by far the most versatile. Not the SD.

Thus all three hulls are "specialists". Only the planing hull can do all three ... to some degree.

 

[RBack]

Art,
I have a friend that calls Starbucks "the office".
An interesting friend.

RBack,
Great analogy but a true SD hull does supremely well at something planing and FD hulls do poorly at. That is running at speeds inbetween planing and less than wavelength speeds. A PU truck and a car do very well at what they do but those half cars half pickups things do'nt do anything well. Same w a motorsailer. Or a hybrid car. But at the speed she's designed for SD hulls are wonderful doing the mid speed thing and what's they are designed to do .... well at. It's not that they ca'nt do anything well. They do the midspeed thing very well.
You wrote;
"Generally speaking the hybrid is a specialist in being a hybrid, thus rather versatile - as already mentioned several times."
Not very versatile at doing very well (higher speeds and lower speeds) but very well at in-between speeds. Can't go high at all and does poorly at low. Does only well at SD. All three only do well at what the're designed for. But the planing hull is by far the most versatile. Not the SD.

Thus all three hulls are "specialists". Only the planing hull can do all three ... to some degree.

Well yes
My analogy was a bit oversimplistic. Strictly hull wise, you're of course correct. I had other aspects in mind as well but anyhow. The "rather" in "thus rather versatile" is perhaps to strong.

 

[Nomad Willy]

Rback,
I loved the way you wrote it. Almost like poetry.
Watching me stumble on this subject one can easily see how hard it is to get it right. There's only one NA here and he's wisely staying out of it.

I flubed up my post earlier in haste. There's only one type of planing hull that can do all three speeds fairly well. That would be a relatively long and narrow or high aspect ratio hull like a long airplane wing. Unfortunately most all modern planing hulls are low aspect ratio .... short and wide. They are more or less two speed hulls as near the hump speed they are rather useless. And so the only one that does all three w some degree of grace and efficiency is a long slender planing hull. Too late I can't fix my post 109 as the edit has expired. -

 

[psneeld]

Well yes
My analogy was a bit oversimplistic. Strictly hull wise, you're of course correct. I had other aspects in mind as well but anyhow. The "rather" in "thus rather versatile" is perhaps to strong.

Actually, I think you were correct in post 106.

Semi anything sounds like a hybrid...something that has the characteristics of 2 different things.....

Stick to your guns...it was good the first time you wrote it.

 

[eyschulman]

Regarding the narrow issue of fuel burn economy and disregarding the other fine aspects of a FD hull I would once again point out that a SD boat designed for max fuel efficiency can blow away a FD boat if issues of beam water line length and weight are given priority in the design and build. Several successful endeavors in this direction have been made down under. The light long WL multi hull is also capable of blowing the socks off a FD re; fuel burn/mile. If I were to build a boat to travel more than 5K for max fuel burn efficiency I don't think I would even consider a FD hull. I think most people who chose FD boats are a lot smarter than putting all the eggs in one basket and are taking advantage of the other fine qualities of FD.

 

[Nomad Willy]

Eyeshulman,
Sure ... if the SD was half the weight. And w typical boats they will most likely be close to that.

And if I had a planing hull that was 1/4 the weight of a FD boat it's fuel burn should be about the same. A plywood planing hull same size as my boat 1/4 the weight would probably have a 3 cyl 25hp diesel and burn less fuel than my boat (1gph). All the above at displacement speeds.

In the bottom of your post did you mean SD instead of FD?

 

[psneeld]

Totally disagree....there are many fine points of design that are being poorly explained.

The whole point of a SD hull is to efficiently carry loads greater than a planing hull and have a much better speed partially loaded than a FD.

Be real careful of what is being posted.

 

[BruceK]

I think the boat and the engines tell your what speed it likes to cruise. It`s not that difficult.

 

[AusCan]

Generally speaking an SD hull is a hybrid.
Generally speaking hybrids are best at being [half] good at several different things.
Generally speaking they (hybrids) will be outmatched by the (various) specialists of each and every category (task) the hybrid can "compete" in.
Generally speaking the hybrid can strike back when it comes to tasks where the individual specialist is no specialist.
Generally speaking the hybrid is a specialist in being a hybrid, thus rather versatile - as already mentioned several times.

In biology it's almost equal to opportunistic organisms (crows, rats, etc.) versus highly specialistic adapted ones (peregrine falcon, anteater, etc.).
And I'm certainly not putting different values to peregrine falcons and crows here.
So don't misinterpret if you happen to own the crow (or rat) trawler.
Your boat will do just fine where/when the peregrine boat fails completely.

... generally speaking.

As the owner of a motor/sail hybrid, I can appreciate this post. Versatility is essential, as the sea has endless variations that we have to deal with.

 

[Art]

I think the boat and the engines tell your what speed it likes to cruise. It`s not that difficult.

Yes... but only if you listen, closely!

 

[ranger58sb]

Chris,
If I wanted to go 6 knots most of the time I'd get a FD boat and go 6 knots. If I opted to get a boat that went 24 knots some of the time I'd either admit I was running my boat in a way it was not intended.

Chris,
Another good point.
And to call out or plan such a design why would you want to go 6 knots most of the time? Your boat design should be centered around that. And also why would want to go 20 knot -art of the time? And when you decide what is more important you look for designs that deliver a design that's slanted that way.

Your missing my meaning. I mean appprox 50% of the time you want to go slow, and the other 50% you want to go fast. Or maybe 33% slow, 34% moderate, 33% fast. Not one velocity most of the time...

Doesn't matter to me WHY you might want to do that; that's a supurflouos question. You do, that's all that matters to my (rhetorical) question.

So how do you find a boat that will do that? If you find a boat that will do that, do you think the designer intended that flexibility?

On another tack: the designer isn't the guy who pays for running the boat... so eventually it's out of his or her hands.

-Chris

 

[Group9]

I just hope everyone is as happy with their hull amd the speeds it can go as I am with mine.