Propeller Selection

I am wondering if any of you prop experts out can help me. I had had various size figures thrown at me and I am confused. I am building a 57 footer fishing beam trawler. The parameters are as follows:

LWL - 52ft
Beam - 16ft
Draft - 5ft
Displacement - abt 30 tons
Hull - Displacement hull (wood construction)
Desired Speed - 9 knots
Engine - 220 hp
Gearbox ratio - 2.95:1 or 3.5:1
Prop type - Bronze (fixed pitch)-4 blade.

What size of pitched prop would give best performance?

Thanking you in advance for your comments

Nabb

Performance.

Speed, efficiency, smoothness, repairability, inexpensive, strength ect ect

I ran your information through 3 different prop calculators guessing at your W/L beam as 15, molded depth as 4, max rpm as 2400, that 220 was a continuous rating & diameter was unlimited.

All seemed to agree that this would be a 10K vessel.

With the 3:1 transmission 32x27, 32x29, 32x25 were the estimates.

With the 3.5:1 34x30, 33x36, 35x29 were the estimates.

All numbers adjusted for 4 blades.

Here's an easy to use and very flexible calculator:

www.vicprop.com/calculator.htm

The Eagle 58 ft, 14 ft beam, 40 tons, single DD natural 165 hp 1500 rpm, cruise 70 to 10 kts, prop 4 blade 38” X 26”, 2.0+ mpg.

Many trawler/tugs turn big slow turning props to push a lot of water. You need to decied if slow or fast turning prop.

Nabb:

That is nearly an impossible question for us recreational trawler owners to answer. If used in fishing and hauling a trawl, then the prop requirements are entirely different from recreational useage.

Find a good prop shop that works with commercial fishing operators and work with them to find the right prop for you.

David

djmarchand said:

Nabb:

Find a good prop shop that works with commercial fishing operators and work with them to find the right prop for you.

David

Click to expand...

Sounds like the best idea of all...

Include the missing items mentioned in my first post and email several manufacturers telling them how you plan to fish your vessel.

djmarchand said:

Nabb:

That is nearly an impossible question for us recreational trawler owners to answer. If used in fishing and hauling a trawl, then the prop requirements are entirely different from recreational useage.

Find a good prop shop that works with commercial fishing operators and work with them to find the right prop for you.

David

Click to expand...

March,
I don't know for sure but I don't see why it should be any different. Get the prop loading right, the dia OK w the hull and available space, rpm at WOT the rated rpm and the most cost effective wheel.
Since fish boats aren't a fixed load vehicle pitch, dia, #of blades would need to be determined for gross load but essentially one does that for a yacht too. It's just that the net weight and gross weight are much further apart on a fish boat. But one would still have to prop for gross.

And I think most sizable prop shops work a lot w both many different kinds of commercial and pleasure boats. There are quite a number of good shops in our area and even in Ketchikan ther'e is a good shop.

manyboats said:

March,
I don't know for sure but I don't see why it should be any different. Get the prop loading right, the dia OK w the hull and available space, rpm at WOT the rated rpm and the most cost effective wheel.
Since fish boats aren't a fixed load vehicle pitch, dia, #of blades would need to be determined for gross load but essentially one does that for a yacht too. It's just that the net weight and gross weight are much further apart on a fish boat. But one would still have to prop for gross.

And I think most sizable prop shops work a lot w both many different kinds of commercial and pleasure boats. There are quite a number of good shops in our area and even in Ketchikan ther'e is a good shop.

Click to expand...

Agree, except the trawling (towing) part takes a lot of power external to the hull and needs some expert factoring in.

Yup I should have re read the post. That would probably require underpropping, maximum near static thrust, largest dia possible, high aspect ratio blades and optimized blade area for optimum area loading.

So I was wrong that it would be about the same process and things to consider as a yacht. And talking to other trawler skippers could be a must. A prop shop in an area where trawlers home port also may be almost a must. Not to do the work but to know how to configure the prop to that application.

The resulting prop would look something like this:

Don't understand why you would query this forum. Presumably you're working from a professional naval architect's plans. I'd query the architect regarding recommended power and propeller requirements/specifications. Consulting various propeller shops might be helpful too.

markpierce said:

Don't understand why you would query this forum. Presumably you're working from a professional naval architect's plans. I'd query the architect regarding recommended power and propeller requirements/specifications. Consulting various propeller shops might be helpful too.

Click to expand...

Be sure the prop shop deals/know commercial, not just pleasure.


Many of the older tugs/trawlers/and even pleasure when the engines did not have the HP and high revs of to day, turned a big/huge slow turning props. Some of the direct drive were down in the 100 to 400 range. Most of the older commercial trawler/tugs build pre 1980 were powered by single DD or CATS under 200 hp that turn about the same size prop as the Eagle.


If sound like he is building a commercial trawler NOT a pleasure, different engine, running gear, prop and hull design. The Eagle was build on a commercial hull, and specifications. That is why I don't and probable never will understand why pleasure boats are so concern about wide open throttle of max RPM? I am amazed that a person would spend hundred/thousand of dollar re propping when they will probable will NOT run at those high rpm’s. Better to clean the hull, redistribute/trim the boat and maintain what they have.

Nabb(the OP) is building a wooden fishing trawler on the East Coast of the African continent. He has asked a few other questions here http://www.trawlerforum.com/forums/search.php?searchid=302745 that lead me to believe there may not be a naval architect involved with this build. Or at least not at the level of involvement most of us would assume.

Frankly I'd love to see pictures of the craft you are building Nabb. If you need help uploading them please feel free to send me a private message and I will send you my personal email address.

Phil wrote;

"I don't and probable never will understand why pleasure boats are so concern about wide open throttle of max RPM? I am amazed that a person would spend hundred/thousand of dollar re propping when they will probable will NOT run at those high rpm’s. Better to clean the hull, redistribute/trim the boat and maintain what they have."

Running at WOT and high rpm is just a test to confirm that the propeller's pitch, diameter and blade area is matched to the engine. And one needs to do the max rpm tests for less than a minute. After one gets the all in balance then all that's necessary is to run as the manufacturer recommends ... anywhere in that range.

Cpseudonym is right no naval architect is involved. The boat builders are a bunch of carpenters who have learned how to build boats. Sometimes I get frustrated when they can not answer technical questions. Thank God they are not building aircraft. As an engineer (not marine) I do not like guess work. That is why I have been asking a lot of questions.
I would appreciate if any of you could give me a lead to some of the manufacturers.

Nabb

Nabb,
I would probably recommend you to get a little professional advice on this matter.
Most trawlers (prawn) down our way run square tip props in a nozzle (it doesn't have to be steerable) to generate more towing thrust.

Cheers
Benn

Benn is correct, get professional assistance. A good place to start might be:

SNAME European Regional Office


c/o Elkco Marine Group
61, Poseidonos Avenue
Palaio Faliro, 17561
GREECE
Telephone + 30 210 4528200
Fax +30 210 4526260
Email: sname@elkco.gr

Key Contact: Petros Lalangas
SERO Director
Email: plala@otenet.gr

SNAME has a very comprehensive library of technical documents which address the issues you are dealing with. The library also includes several good studies on proplusion efficiency and propeller selection for "trawler style" yachts in the same size range.

There is very good information available. Though it might cost $20 or $30, it is certainly worth it.

I would like to thank every one for their advice on how to address the prop selection problem. Based on your advice I contacted Mr. Robert Olds in Australia and has helped in selecting the appropriate prop for my kind of operation. This is a great family.

My regards to all.

Nabb

Hi, I am looking for replacing my propeller and gear ratio and found theses sources very interesting

http://www.fao.org/docrep/x0487e/x0487e04.htm
http://fr.scribd.com/doc/32231281/Propeller-Handbook

The problem is the more information you get the more difficult it is to make choice.
Now I am looking into Kort nozzle