Hull Shapes----Show us your girl's bottom

[North Baltic sea]

Hmmm, data?

Sorry no data, but
The number of blades affects propeller efficiency. The less blades in the propeller the more effective it is. The efficiency is due to the fact that each blade faces in the water an obstruction that slows down the rotation of the propeller and thus the speed. A single individual propeller would be the most powerful possible. In practice, however, it is impossible, as the vibration caused by it would be completely uncontrollable, not the components of the engine, and none / no one else could withstand it. A three-ply propeller is a compromise with blades. The number of blades also has an impact on propeller thrust properties.

The more blades propeller has a greater pushing effect on the water than with a lesser-rounded. Thanks to good thrust performance, multipurpose propellers are mostly used in heavy boats and in water jets. Larger (4-5) pivoted propellers are more economical at three speeds at mid / trip speeds, but at high speeds, the blade resistance increases dramatically and reduces efficiency for a 3-blade advantage

Here would be a good way to improve the propeller's benefit ratio, the miracle that you have not used a pleasure boat to enhance your safety and efficiency?

Maximising Propulsion effeciency

NBs

 

[Nomad Willy]

It’s not really a question of the number of blades but a question of the blade aspect ratio.

If you have a given amount of power and prop speed if you increase the number of blades the blade area will need to be reduced per blade. That will automatically increase the aspect ratio (width of blade compared to the length of blade). Small high aspect ratio blade are generally not available. Most boats have too much power for such a prop. So going to more blades means increased diameter .. usually. But also usually there is no room to swing a larger dia prop. That is almost always the reason to increase the number of blades. The three blade lacks the blade area for the amount of power. That is almost always the reason for a 4 blade prop on a rec trawler.

But I’m just babbling about something I only know a little about. A good prop man will be able to tell us how many blades are best. And variables like power, dia space, shaft speed and boat speed determine the prop and the number of blades is the result of these variables. Not the other way around. The variables choose the prop. And if the boat owner says he wants a 4 blade instead of a 3 blade the result will likely be a prop without enough pitch. This will result in too much parasite drag from too much surface area. Lots of dia is thought of as being more efficient but if if the pitch/dia ratio is not in the “best” zone/range and efficiency will be less than optimum. For most trawlers three blade props are best. The prop man (engineer preferably) should decide the number blades. Not a boat owner.

 

[Art]

Maximising Propulsion effeciency

NBs

Thanks for the link... Items therein make me ponder...

Would the drag ratio created by thin keels on each side of twin screw planning hull be offset by Kort Marine Nozzle improved efficiency??

 

[Donna]

Thank you johnP

 

[psneeld]

thought I posted this before...courtesy of RickB

5 attempts at rotating, and saving failed...enjoy it sideways....

 

[Nomad Willy]

Art,
I would think the in-efficiency is largely a product of the prop blade to nozzle clearence and the drag of the entire nozzle. The prop blade tips to the nozzle clearence needs to be really small to have any gain at all.

 

[Art]

Art,
I would think the in-efficiency is largely a product of the prop blade to nozzle clearence and the drag of the entire nozzle. The prop blade tips to the nozzle clearence needs to be really small to have any gain at all.

Hey Eric - Thanks for input.

My understanding may be incorrect re what is mentioned on the link Maximising Propulsion efficiency Seems to me that efficiency increases up to around 15 knots. My misunderstanding may be that the mentioned efficiency increase only represents he difference between two models of nozzle... and does not represent an increase over open props that are using no nozzle?? See bold paragraph about 1/2 way down.

Quotes from link:

"Originally a nozzle was not considered practical for vessels operating above 10 knots, simply because it required more power than an open propeller. Today, Rice Speed Nozzle systems are in use for vessel speeds up to 15 knots. To better understand this technology, we first need to revisit the concepts of how propulsion is achieved, thereby allowing the maximizing of these to our advantage."

and

"Running open propellers when a nozzle will save 22% fuel or more on most trawlers, fishing and tuna vessels up to 15 knots."

"HOW PROPELLERS WORK - The High / Low Pressures of Propulsion

Let us freeze a propeller in motion. With right hand rotation, the propeller blades will rotate clockwise viewed from behind. As the blades push down, water is forced down and back, as is done by your hand when swimming. Because this motion has created a space, water must rush back simultaneously to fill the void resulting in a pressure difference between the two sides of the blade. There is a positive pressure or pushing effect on the driving face of the blade, and a negative pressure or pulling effect on the front face of the blade. As the propeller rotates, it draws water from its front through an imaginary tapered cylinder a little larger than the propeller diameter at the front. As the water passes through this imaginary cylinder, the water accelerates as it passes through the narrower end of the cylinder. This acceleration of water results in the force that we know as thrust.​

HOW A NOZZLE WORKS
To obtain the most thrust, a propeller must move as much water as possible in a given time. A nozzle will assist the propeller in doing this, especially when a high thrust is needed at a low ship speed. As we already know, as the propeller blades rotate in the water, they generate high-pressure areas behind the each blade and low pressure areas in front, and it is this pressure differential that provides the force to drive the vessel. However, losses occur at the tip of each blade as water escapes from the high pressure side of the blade to the low pressure side, resulting in little benefit in terms of pushing the vessel forward. The presence of a close fitting duct around the propeller reduces these loses by restricting water flow to the propeller tips."​

There are additional important items on the link. I need to read it carefully again!​

Art ​

 

[Robvald]

Bottoms up

Here are some photos from the my survey haul out and during price negotiations. 2 years and still a work in progress but she is coming along nicely. 1150 miles in 2017 in SF bay and delta. I wish that I had more time and $$.

 

[Art]

Here are some photos from the my survey haul out and during price negotiations. 2 years and still a work in progress but she is coming along nicely. 1150 miles in 2017 in SF bay and delta. I wish that I had more time and $$.

She looks nice... Enjoy!!

 

[Scottbwheeler]

Salt Wife Bares All!

44 Endeavour Trawlercat

 

[Bigsfish]

That’s all I got.

 

[Bigsfish]

 

[Nomad Willy]

44 Endeavour Trawlercat

Interesting Scott,
How is this tunnel functioning? As a square tunnel drive? A lets protect the prop at all costs? Or as greater efficiency?

Looks like the pic is of the port hull w the stbd ahead to the right. So I assume the stbd hull is the same.

 

[Scottbwheeler]

Interesting Scott,
How is this tunnel functioning? As a square tunnel drive? A lets protect the prop at all costs? Or as greater efficiency?

Looks like the pic is of the port hull w the stbd ahead to the right. So I assume the stbd hull is the same.

Hi Eric,

The running gear and rudders are protected, with the pockets my draft is only 3’ and I can sit on the bottom with no worries.... as I found out when Hurricane Irma sucked all the water out of our Bayou! Both hulls are the same. I can’t speak to the effect on efficiency.

Here’s a lightened picture which better shows the box:


Regards, Scott

 

[AusCan]

I just finished a bottom job, and took a couple snaps today.

The side profile is in down under profile.

 

[Art]

Pretty!

 

[Donsan]

44 Endeavour Trawlercat

That was one of the reasons we loved the Endeavour Trawlercat. The almost 20' beam, not so much.

 

[Scottbwheeler]

That was one of the reasons we loved the Endeavour Trawlercat. The almost 20' beam, not so much.

The beam is a bit of a beast, but makes for a stable platform. Fortunately we are rarely in a marina where it would be a potential issue depending on slip availability. My neighbor was actually looking at her but decided it was too wide for his dock, the minute he decided against it I swooped in! He opted for the 40’ Endeavour Trawlercat with a 16’ beam.

 

[warren]

Unprotected props

Your well protected props will thank you
Check out from about 10:30 onward
https://youtu.be/kQi0wASVQ1Q

Later they are looking around a boat yard that has your type cat in it!
Cheers Warren

 

[cardude01]

So about the rocks in Okeechobee, did these guys in the video leave the marked channel for some reason going across the lake and hit rocks? Or were the rocks in the channel? I’ve been across a couple of times and always had deep water in the marked channel.

 

[Bigsfish]

CD

I’ve been across lots of times and never seen a rock but friends who have hit seem to cut the turn near the western side a little short. Not sure if this poster did that.

 

[BruceK]

I just finished a bottom job, and took a couple snaps today....

A real FD hull, no wonder it slips through the water so easily with modest power. I have followed a friends Resort 35, same boat just bigger,they roll easily, but very safe boats in bad weather. He took his from Sydney on a 20 mile ocean transit north to Broken Bay in poor sea and wind conditions, I squibbed it and spent a night in harbour before heading out.

 

[Sabre602]

Our old converted fishing boat, cold molded by a guy (Bob Hadden) in Sechelt, British Columbia in 1976. He built a half-dozen or so of them. I have no information on the designer, but wonder if it was a Monk-inspired design. I haven't seen the underbody of a Roughwater up close, but she looks similar to me. Kingfisher is 37 feet, with a 10.5 foot beam and 4 foot draft. She was an honest fishing boat...if you look closely you can just make out a big vertical iron member through-bolted to the after part of the keel, all that remains of the cage that surrounded the prop, meant to prevent fouling of nets and lines.

 

[Nomad Willy]

I just finished a bottom job, and took a couple snaps today.

The side profile is in down under profile.

AusCan,
Our boats are very similar.

 

[AusCan]

AusCan,

Our boats are very similar.

They certainly are, Eric. Your stern may be slightly more canoe shaped, whereas mine is perhaps a little bit more rounded, but it’s almost a mirror image.

I’m guessing mine might be a tad more rolly if I didn’t have the rolling chocks.

 

[Art]

Aus, Nomad - You guys gots kissen cousin boat bottoms!

 

[tozz]

Hey Eric,

Have you ever run over any bow pickers gil nets.

I was coming into Eshamy bay and the place was full of bow pickers with cork floats and nets all over the place. With the light fading fast I couldn't see some of them. I almost ran right over a string of floats.*

I see there little tenders for the seiners with the skeg just drive over the nets. (They look like bathtubs with a motor.)

*Wondered if your boat would do the same.

That prop looks well protected.

SD*

Last haul out I installed line cutters.

 

[rswift]

Not a true trawler but learning to travel at trawler speed. Keeping that bottom clean does help to extend the range.

 

[senangsekali]

 

[Simi 60]

Going back in near two years ago