True displacement models

[eyschulman]

Hey guys your boats have similar WLL but look at your displacement and buttock lines ... the angle of the bottom aft as seen in Ted's pic on post # 161. (top of page).

Ted's FD boat probably weighs 4 or five times your SD (close to planing) hulled boat. All the factors are players in the classification of hulls. But as Tad says many are impossible to classify. eyeshulman's boat is SD but it may have a straight run aft so is not in the middle ofthe SD range. So Ted's boat is at the left end of FD and eyeshulman's boat is at the right end of SD. So they are considerably more different than SD and FD.

As always just an opinion. What's yours?

Oh yes I see the rudder Ted. Looks a bit bent but straight enough to do the deed I'm sure.

Now I've got to figure out how to copy Tad's post have it handy.

Very different bottoms and weights but look at the wakes at sub hull speeds. Both look good and both are probably in good fuel burn ranges no matter where they fall on the FD SD scale. The point I repeat and champion is that a SD boat run at sub hull speeds(basically in FD mode) will run much like any displacement boat of similar length beam and weight and probably better than the real heavies.

 

[Nomad Willy]

I agree Eyshulman.
Look at Ted's wake in his avatar. It shows him running at a bit more than half of his hull speed. At near hull speed there probably is a huge difference in efficiency but below that it dosn't make much difference. Look at barges weighing hundreds of tons being towed by a tug that is tiny compared to the barge. And they go much faster than my Willard.

 

[Ken E.]

If you can get Hargrave on the line there is a future for you as a medium!

Put 300 horses on that Willard and see what happens. Or tow it with a big tug, what do you think happens then, stops the tug in it's tracks?

I guess it all depends on what you or I mean by "way". And Hargrave meant by "bad place".

A buddy had a 42LRC, at WOT maybe 10 knots and very very ugly, there in that "bad place".

Hargrave also designed many planing hull Hatts with hard chines, mine included. While not nearly as efficient at displacement speeds as SD or FD hulls, mine is actually pretty clean through the water at hull speed, ~ 7 something kts ( .....I can feel the heat of getting flamed already....). Beyond hull speed, fuel consumption goes up exponentially as the stern squats and big waves are formed.

I like eyeshulman ' s comments about not getting hung up on hull type but rather what you need the boat to do for you. I like a big cockpit for fishing and as a patio when on the hook, which a sportfish design is perfect for. Not a trawler, but I run it like one.

 

[psneeld]

Hargrave also designed many planing hull Hatts with hard chines, mine included. While not nearly as efficient at displacement speeds as SD or FD hulls, mine is actually pretty clean through the water at hull speed, ~ 7 something kts ( .....I can feel the heat of getting flamed already....). Beyond hull speed, fuel consumption goes up exponentially as the stern squats and big waves are formed.

I like eyeshulman ' s comments about not getting hung up on hull type but rather what you need the boat to do for you. I like a big cockpit for fishing and as a patio when on the hook, which a sportfish design is perfect for. Not a trawler, but I run it like one.

No heat...actually for once many members see that there are no magic numbers for hull designs, there is crossover and any hull run in the displacement mode that avoids the big drag items will be close in efficiency if the engine(s) used aren't way off the scale in terms of HP.

 

[Nomad Willy]

Close as in less than twice as much drag.

But that's only the typical trawler hull and there are quite a few close to FD lines that have less drag at Displacement speed. And displacement cruising speed is about one knot below hull speed. But many SD hulls do well at hull speed and slightly above especially if they are narrow or light or both. Lots of variables.

 

[psneeld]

You said it ...lots of variables.


Nice to see that finally recognized.

 

[Nomad Willy]

You got it ...

 

[burntheships]

1973 Fales Trawler 30

Can anyone tell me what the hull configuration of this boat look like?
1973 Fales Trawler 30
does it have an aft keel? like some other trawlers? any pics???

 

[Brooksie]

It's a 30' Willard, usually stretched to 33'. which should be easy to find pictures of.

 

[OldDan1943]

After a while, all trawler exterior views appear to be the same.

 

[Crusty Chief]

Jeeeez, I forgot about this thread......and my head still hurts. The OP probably gave up and bought a ranch in Montana.

 

[Nomad Willy]

Here are some pics.

 

[Nomad Willy]

Hull broadside.
Exposed to favor the hull.
The railing aft is on the next vessel.
This is a 30’ Willard. Not a Fales. The Fales is just a little longer.

 

[Plane Nauti]

Eric,


Why would the keel no be faired just in front of the prop? It seems the prop would be more efficient with smooth water at the 12 and 6 o'clock position.



Thanks....


Keith

 

[Nomad Willy]

Keith,
In some other ways the W30's were less efficient than they could have been for various reasons and design compromises. I put a 5 blade prop on my boat looking for smoothness and efficiency but it didn't work out.

Many see the FD hull as solely a path to fuel efficiency.
There's much more to FD than a low fuel burn. A pleasant motion at sea, greater directional stability and abilities running in following seas and others like the ability to carry much more weight w/o burning much more fuel.
All the Willards I've seen have an 18" prop but there's room for a larger prop. A smaller faster turning prop offers flexibility that can't be had w a larger dia slower turning prop. That's why they use small props on outboards. The designers don't know ahead of time what type of boat the outboard engine will be used on.

Any design (especially a boat design) has many priorities and objectives to achieve. And seldom at the complete loss of any one objective.

So yes the keel's trailing edge could have been scalloped to reduce turbulence for the prop in-feed but other priorities like building costs, mechanical vibration keel strength, or whatever. More than likely they built the mould from a wood structure w the idea that scallops could be done later. But they didn't get around to it .. so the saying goes.

But the difference I'm quite sure at 6 knots is fly stuff. And they probably thought so too.

I know of one Willard 30 owner that did cut his keel out and laminate scallops into the TE. He's from Maine. Haven't talked w him since he launched his boat so don't know if all the work produced wonderful results or not.

Here's another FD hull w long high a aspect ratio prop. And the dirty square cut off keel trailing edge.

 

[Fletcher500]

Interesting thread. I ordered Dave Gerrs, Nature of Boats, hull design book to dig in to the finer details. Good technical insights from Tad Roberts, Naval Architect, and others who know the practical side of hull shapes.

 

[Nomad Willy]

Fletch .... and ...