Displacement boat - speed

https://www.youtube.com/watch?v=SJXHclkDOZM

 

The stern on the Poseidon 25 is much wider & the maximum width of beam is extended further aft than the vessel Duco84 has. WindRaf also writes those fatal words " and you can install more power".

Were it me, I would sell the boat to someone who would be content with its character & build a Lumber Yard Skiff. Look at #6 & #14 in this thread.

http://forum.woodenboat.com/showthread.php?138899-lumber-yard-skiff&highlight=jclays

https://www.google.co.uk/search?q=l...&ei=LjAqVfcD19pqw6qAoAs&ved=0CCAQsAQ&dpr=1.88

The plans are only $60. http://www.oldwharf.com/ow_workskiffs.html

Use whatever reasonable WBP plywood you can get hold of, build it quickly & take it out on the water. A 50 hp outboard will push it to 50 kph. A month from now you'll be a happy sailor. Take a bit longer & build a pilot house on it, if you want.

http://www.thehulltruth.com/attachm...ritime-skiff-2090-w-pilot-house-sold-ms33.jpg

http://s383.photobucket.com/user/kevinmorin_photo/media/Pilot House/pilothouse_terms_1a.jpg.html

Good luck.

 

........

Pericle

...is this the point.

 

We has a phrase in English that says it all. "You cannot make a silk purse out of a sow's ear". You might know something similar. "Non puoi cavare il sangue dalle ****".

Some tasks are not worth considering. "By knowing things that exist, you can know that which does not exist." Miyamoto Musashi.

 

The slender stern sinks more than a transom stern does when the boat is pushed hard.

Plates will help stop the stern squat , but any real speed increase will be minor , tho the stern wave will be smaller.

Perhaps 1/2 K faster at top speed . .

Herrishoff did plates to some of his canoe stern boats , not very successfully.

 

There are some really fast double ended boats in Finland. They tend to be quite light and have a lot of power.

This one is probably the fastest reaching 40 knots: http://www.friddemartin.net/fakta

This one "only" 25 knots: http://www.nettivene.com/moottorivene/fiskari/544748

Both have very much modified hulls and perform almost like planing boats.

The boat discussed here is large and probably heavy and has a too small engine to be a semi-displacement or a planing boat. Why not just travel at 6-8 knots with rather low fuel consumption?

 

I will be satisfied with 10kn as max speead and I hope better stability. Definitely it is possible to achieve higher speed with displacement hull by adding sponsons (Menorquin). Before 15 years on subject boat I had engine with 40hp and I achieved almost same speed as with this one, 100hp. For now sponson, after that probably engin with more power.

 

I have some experience with ideas along these lines, have a patent for one and several designs incorporate it. A European builder is now incorporating similar into their power craft, as well.

In a nut shell, these wings (as in my case) or shelves, work only within certain speed ranges, on certain hull types and unless adjustable (computer controlled) are just drag, in the other speed ranges the hull form may operate in. My approach was to modify the stern wave to permit semi plane speeds, with less power and over a longer range without significant trim changing, at least as much as it would without it.



This shows the asymmetric foil aft, which delays unacceptable stern squat, permitting speeds higher into the semi plane mode, without excessive trim angles chewing into potential and efficiency. Again, it's effectiveness is limited and across a fairly narrow range (if fixed), plus it takes a good bit of knowledge, experimentation and testing to get is remotely close to effective.

 

I wonder how the guy who changed engines out felt about only getting 2 kt extra out of her?

 

Im just guessing but maybe his current motor is not loaded enough a change of gearbox to 2:1 may improve speed

 

Hey PAR, what and where is the "asymmetric foil" you speak of in that picture ?

 

Yeah, Paul,

I would like to see how your solution works and see how it differs from what I use and what Walt Shultz has at Shannon Yachts?

 

the concept is this

http://www.ayd.it/press/Nautica_n-613-maggio-2013/Nautica 613 maggio 2013.pdf

 

That boat appears to have a planing hull bottom. At planing speeds with water separating at the chines the shape above the chines does not affect performance.

 

Yes, as I said they are heavily modified.