Now I understand.
FD Bottom:
1. Rolls like a log in water.
2. Put 10,000 HP engine on one and it will never plane but the end result and accident report will be spectacular.
3. They go slow.
Any more questions please advise.
Just to keep this rolling, there are many SD vessels that are great and proven blue water vessels. It would be a tough call to say a FD Nordhavn 64 is a better blue water vessel than a SD Fleming 65.
Actually, if you could mount a 10k hp motor on a log, it would be quite fast, assuming the log is straight and missing the branches. Due to the waterline x beam ratio, a log (or a telephone pole) would be quite fast through the water.
My opinion of a displacement boat is one that sits in the water and when you move it, you apply pressure in the direction you want the boat to go and let the water flow out of the way and around the hull. Since water is thicker than air, you have higher resistance and therefore are limited to the speed you can move the hull. If you mounted the 10k hp engine on the hull, you would eventually push it out of the water and make it a planing hull, skipping across the water.
Just to keep this rolling, there are many SD vessels that are great and proven blue water vessels. It would be a tough call to say a FD Nordhavn 64 is a better blue water vessel than a SD Fleming 65.
I think Beebe had a pretty good definition of trawler (if I recall correctly) - a bluewater vessel capable of crossing oceans under power. No mention of hull form, although all of his boats for that purpose were FD.
Yup .. didn’t read all of Fish53’s post.
FD SD have nothing to do w performance or speed.
It has only to do w hull form .. the shape of the hull aft.
How 'bout these buttocks?
So...
What is the definition of full displacement.
Is it a specific hull design? Where no matter the engine HP it will always stay within the FD formula. Hull Speed = 1.34 x √LWL
Or
Is is a boat with a limited hp power plant that can never exceed FD speeds based on the LWL? Even if that hull design with bigger engines would result in a boat that would exceed the formula!
Can you even describe a FD bottom?
Yup .. didn’t read all of Fish53’s post.
FD SD have nothing to do w performance or speed.
It has only to do w hull form .. the shape of the hull aft.
You can’t change that w/o lots of cutting ect w tools to change the shape aft. Your boat is SD whatever speed she goes.
By the way I really like your boat.
But 5000hp and 100knots Fish I think it would be safe to call it a planing hull. I know of no SD hull that I’d bet would be controlable at 100 knots. But most trawlers (SD) would go about 20 knots w 3-400hp. So a SD boat could go at medium slow planing speeds. Medium planing of 18 knots for CptnPete’s west Cove and would be easily attained by hp alone.
9 knots. Pretty good for 100hp.
Nice looking hull from what I can see w the black hull paint.
Ahhh towing the net.
Do you tow into the tide?
Don’t see how it could be done any other way.
But I also have a hard time imagining towing those huge nets w much tide current.
I usta work at False Pass in the Nick Bezz days.
Really...
I would think that would be an obvious no brainer.
I know the Fleming is a highly respected boat but I’m having trouble imagining it in 12’ following seas and matching the Nordhavn for comfort and safety.
This is one of the fishing trawlers I used to own, she had 260hp but was designed originally for 100hp. Mine would do 9kts WOT, one with 100hp did 9kts WOT. Of course the hp was to tow a bigger net and mine weighed 50,000 lbs. View attachment 85078
That's what has me scratching my head a bit. Your CD38 (which i really like) has a very similar hull shape to my WC40 from what i can tell in the pic you have shared and the marketing brochure i have on it. Same Royal Lowell designer. Same beam. Different displacement (mine is half). And the CD has an extra foot of draft. But I wonder if your Iroquois had no trawl gear, nothing in the hold etc. and had a 200-300HP engine if she too would easily get up above 10knts like a SD. I dont know if the CD had ballast. Nor if it had an extraordinarily thick hull so i wonder where the weight came from in standard out of the box FD configuration.
Of the well known SD trawlers (under 50’) what boats are in the near perfect catergory for offshore running, do you think?
When a wave speeds up it gets longer, not necessarily higher. The height has more to do with the object creating a wave, it's displacement and shape. A planing boat creates a bow wave, the trough is well behind the transom. As a hull without a lot of lift speeds up, the wave it creates is the same length as the planing boat at the same speed but the energy required is much higher, and that energy is spent in building a higher wave.When a wave speeds up, physics dictates that it get higher. Go fast enough, and the stern wave is large enough that the stern sinks into a fairly deep hole, eventually going under.
The unique thing about a "Full Displacement" hull is that it cannot ever climb over it's bow wave, no matter how much power you apply. This means you can never get up on plane and your speed will be strictly limited by the length of your hull at the waterline.
There's more to seaworthiness of a boat than just hull shape....
More than of a few of all hull shapes and boats less yhan 100 feet have crossed the Atlantic. Some a stunts, and promotions with safety boats...but sso have regular joes in things like production sportfish, etc.