Reply
 
Thread Tools Display Modes
 
Old 06-07-2011, 09:41 AM   #21
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,724
RE: Calculating hull speed.

Don't recall a CPP being mentioned in Bebb's book. I think they are too expensive and not as efficient as fixed pitch propellers. I've never heard of anyone on TF saying they have a CPP*** .....not even you Fred. Nobody or almost nobody has one so there must be something terribly wrong w them so why talk about then. Well** ....you do make a good point w the example you often give. AND they are only beneficial on over powered vessels. If one was running their full disp hull w an engine at 75% load the benefits from a CPP would be almost zero.

Fred says "are the ones that carry 50 or 100% more power than displacement cruising require". Willard even overpowers full disp boats. A Willard 40 only requires 23 hp to go 7 knots and they have a 135 hp engine. Easily twice the power it needs or should have. My Willard 30 was blessed w a much better power loading. It's overpowered but not by much. And I cruise at a power loading of over 50%*** ....probably 60%.

*
__________________
Advertisement

Nomad Willy is offline   Reply With Quote
Old 06-07-2011, 09:17 PM   #22
Guru
 
bobofthenorth's Avatar
 
City: Cowichan Bay, BC
Country: Canada
Vessel Name: Gray Hawk
Vessel Model: Defever 43 Offshore Cruiser
Join Date: Oct 2009
Posts: 570
RE: Calculating hull speed.

I'm in the middle of a re-read of the 3rd Edition of Beebe (the "Nordhavn" edition).* There's some limited discussion of alternate drive systems in the section on the work of other designers but that's the only reference to variable pitch props I recall.

*
__________________

bobofthenorth is offline   Reply With Quote
Old 06-08-2011, 03:51 AM   #23
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,537
Calculating hull speed.

Starting at $10,000 it takes a load of hours for a CPP to be worth while.

There were Sweedish 25 boats that had single cylinder Saab (Norway) installed about 30 years ago.

This was std on the Euro fish boats , even as small as 25 ft.
The prop was "paid " for by having a gear reduction but no shifting tranny , the pitch was simply sett for fwd or aft as needed.

Most of our boats were built when fuel was far cheaper , so no thought was ever given to $10K items for a 200 hour a year boat , payback would be in decades!

Today , if we do not release the 85% of US energy reserves locked out be our rulers , $4.00 a gal may not hold and the economics of a more sophisticated drive train will be marketable.Along with skinny boats and light weight construction.

While it is important to match the PC to the boats cruising speed , it will not change the "hull speed" an Ipta.

It certainly does change the POWER required to get there , but like a foul bottom , power and LWL detirmines hull speed.

The difference ( in efficiency at reduced loading )may be very small and if it is the overpropping may not be worth the risk ov damaging one's engine.

Nighel Calder found up to 300% difference on smaller engines.

At full tilt one of our engines might produce 18hp for a gal of fuel.

Slowed down or lightly loaded* to 20% or 30% of rated power it may only make 10 hp* or even 6 hp from that gallon.

The cruising prop , CPP or a 2 speed trannyare ways to properly load the engine at less than WOT , where most choose to cruise.

*

A great example of this came from one of our folks that yanked an old old* diesel, and replaced it with a modern noisemaker.

He seldom used the full KW either unit produced, and was amazed (and saddened) that the fuel consumption went UP!


-- Edited by FF on Wednesday 8th of June 2011 04:02:37 AM
FF is offline   Reply With Quote
Old 06-08-2011, 07:55 AM   #24
Guru
 
motion30's Avatar
 
Join Date: Jan 2010
Posts: 740
RE: Calculating hull speed.

on my lehman powered marine trader there is less the 2mph difference between cruise speed and wot guess there is not a lot of extra power there I am always amazed to see a 40-45' sail boat with that tiny little prop they use Hell the one on my trader is 22'' diameter and some of those sail boats are faster under power with like 65-75 hp
motion30 is offline   Reply With Quote
Old 06-08-2011, 08:10 AM   #25
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,724
Calculating hull speed.

Fred,*

I remember the Saab reversing and variable pitch propeller. I looked at an old wood boat in a barn that had one. "Nighel Calder found up to 300% difference on smaller engines." Don't believe that. That would mean someone w a 40' trawler and a Lehman could match my Willard's fuel consumption*** ....not likely. "with a modern noisemaker." You mean diesel? I agree w most of the rest except the political or OTDE part.

boat9,

"semi wallowing" was Fred's expression. I was quoting Fred and never would have said that. But I have an opinion on what that might mean. I think the full disp boats are the wallowers and as soon as one gets going fast enough so the froth over the stern on a SD or planing hull disappears and "clean" water appears there's a dynamic stability that replaces the wallowing sensation and I think it feels much better."If it doesn't drag*fishing gear, it's cruiser...regardless of hull type." I agree. I agree w Fred and think trawler is a pretentious word and we should be known as heavy cruisers.

Motion,

Yes it is amazing. So if we want real efficiency sailboats can show us the way.

David,

On the graphs you're looking at I think all the numbers there are calculated at WOT. I'm not very sure about this and would like to know I'm wrong. Please advise.


-- Edited by nomadwilly on Wednesday 8th of June 2011 08:20:20 AM
Nomad Willy is offline   Reply With Quote
Old 06-08-2011, 09:48 PM   #26
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,724
RE: Calculating hull speed.

I am a bit ignorant here as I've mostly looked at engine brochures and they seem to have the curve developed from max hp at each engine speed. Is that correct? But one cannot predict with great accuracy the fuel burn of an engine in a boat as the resistance of each boat is different or very different. My Willard (for instance) has very low resistance at half rpm whereas a planing hull may be "on the hump" and have great resistance. How do the curves you speak of accommodate this variable? I'll go on BD or my Mitsubishi site and look at some curves and see what I can learn. Thank's for your input Larry.
Nomad Willy is offline   Reply With Quote
Old 06-09-2011, 03:52 AM   #27
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,537
RE: Calculating hull speed.

"Most diesel engine manufacturers (Yanmar included) give a wot curve (the upper one), a prop horsepower vs rpm curve (the bottom one which is just a mathematically derived 3 exponent curve), and they give a fuel consumption versus rpm curve to go with the prop curve."

Not what I find in brochures.

Yes the left side is power observes (or useable ) on a dyno .

The right side is a math creation of some theoretical prop, not yours.

The usual graph on the bottom is the fuel burn from thew actual output at various rpm , so gen set , pump mfg can use the info.

THe ONLY useful graph for folks that want to set up a boat for cruising at various RPM is called a Fuel Map, or BMEP graph.

This is harder to get than build instructions for a T-88 nuke.

The graph looks like a set of clouds , one on top of the next.

The inner is the lowest fuel burn , at various rpm , The Sweet Spot" that give the best HP per gallon.

Next out is poorer , but still a goal to shoot for , and as the "cloud" outline gets to the 4 th or 5th ring the efficiency is poor , but might be required , long term ideling , or big load like climbing on the plane.

Most of the "prop curve" graphs are rotten to attempt to chose a prop and operating RPM for a specific engine .
FF is offline   Reply With Quote
Old 06-09-2011, 08:37 AM   #28
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,537
RE: Calculating hull speed.

4BY2-150 Version: 2009-09

I am unable to move this to this site to discuss it.

Perhaps a better computer person could move this or any other set of graphs , so they can be discussed?
FF is offline   Reply With Quote
Old 06-09-2011, 11:01 AM   #29
Guru
 
skipperdude's Avatar
 
City: Whittier AK
Country: USA
Vessel Name: Apache II
Vessel Model: 1974 Donald Jones
Join Date: Oct 2007
Posts: 3,147
RE: Calculating hull speed.

With my cat 3208. 210.hp. and a full displacement hull.

*I have a 24" rh 18 pitch prop.

How would I calculate the right prop to give me the proper load on the engine at hull a speed of 7.46 knt p.h. as calculated at the sq rt of 31 X 1.34.

I would like to run at about 75% of WOT. for optimum performance on the 3208

SD
skipperdude is offline   Reply With Quote
Old 06-09-2011, 01:53 PM   #30
Guru
 
skipperdude's Avatar
 
City: Whittier AK
Country: USA
Vessel Name: Apache II
Vessel Model: 1974 Donald Jones
Join Date: Oct 2007
Posts: 3,147
RE: Calculating hull speed.

According to the abstract of title it is 20,000# add another 5,000 for load and I am running 1600 to 1650 rpm at hull speed.

The best I can get at WOT is 2550 rpm.

So*I think I have a prop issue. She is an X commercial fishing boat with a10,000# fish hold so I think it was propped to haul some weight.

If I push it up to 2,000 I am burning about*4 GPH and doing*8 to 8.5 knts

Thanks

*

*
skipperdude is offline   Reply With Quote
Old 06-09-2011, 02:29 PM   #31
Guru
 
skipperdude's Avatar
 
City: Whittier AK
Country: USA
Vessel Name: Apache II
Vessel Model: 1974 Donald Jones
Join Date: Oct 2007
Posts: 3,147
RE: Calculating hull speed.

It wasn't USCG it was the abstract of title that the boat builder issues at the time of delivery.

When I do kick her up to WOT I blow black smoke. I don't think I like that.

SD
skipperdude is offline   Reply With Quote
Old 06-09-2011, 06:16 PM   #32
Guru
 
2bucks's Avatar
 
Join Date: Oct 2007
Posts: 698
RE: Calculating hull speed.

Talk to a prop shop the next time you haul out.

David

Just an added thought from the harsh teacher, experience. Talk to the prop shop before you haul out. find out the questions they will ask about top speed, rpm, temp, etc. Then you can run your boat find the exact answers which will allow the prop specialist to give you the best advice.
2bucks is offline   Reply With Quote
Old 06-09-2011, 10:37 PM   #33
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,724
RE: Calculating hull speed.

Skipper,

I went back in the photo album and found your boat pics on page 14. You're boat is not a full disp hull. It's not even a semi-disp hull. It's got a straight run aft w her chines parallel to the waterline. Only planing hulls have that feature. It may even have a very slight hook in the bottom. If it was a FD hull it would take about 40 hp to drive her at hull speed but as it's a planing hull it should require 80 to 100 hp. Actually I think your boat may be a Tollycraft. Every part of the shape of the hull looks Tolly to me. You say it's "tippy" without the stabs down and that's what they say about Tollys. They have flare all the way to the transom w that little knuckle 5" below the gun'nl that's in the the transom as well. Is there a Tolly in your area?
Nomad Willy is offline   Reply With Quote
Old 06-10-2011, 03:42 AM   #34
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 16,537
RE: Calculating hull speed.

"I wouldn't pay any attention to the USCG tonnage. It is all based on a formula and has little relationship to the real world."

The CG tonnage is accurate , BUT, it measures volume not weight.

Sounds like someone has installed a cruising prop for you.

No need to ever see 2600rpm , only to go to full throttle , record what it is , and never operate higher than 300 below full throttle.

I would paint a red line on the tach at 300 down and simply enjoy the fuel savings . longer engine life and lower noise level.
FF is offline   Reply With Quote
Old 06-10-2011, 10:35 AM   #35
Guru
 
skipperdude's Avatar
 
City: Whittier AK
Country: USA
Vessel Name: Apache II
Vessel Model: 1974 Donald Jones
Join Date: Oct 2007
Posts: 3,147
RE: Calculating hull speed.

Quote:
nomadwilly wrote:
Skipper,

*Actually I think your boat may be a Tollycraft. Every part of the shape of the hull looks Tolly to me. You say it's "tippy" without the stabs down and that's what they say about Tollys. They have flare all the way to the transom w that little knuckle 5" below the gun'nl that's in the the transom as well. Is there a Tolly in your area?
*Eric, I searched long and hard to find out Just where the hull cane from. One person from the Tollycraft web site told me that Tollycraft did not make a 32 ft hull but sdold a 28' mold to Glassply and Glassply built and sold bare hulls after streching the mold.

The carpenter who built the boat A Donald Jones of Tacoma Washington. Bought a hull and built the boat on it. This is all hearsay but you seem to validate the assumption. All is purley conjecture but you may be right on with your statement. Here are a few pics of the boat taken in 1992 for a survey done at the time. Other than the paravanes and the bilge keels it may be a Tolly hull. Don't know for sure.
Attached Thumbnails
Click image for larger version

Name:	apache13.jpg
Views:	65
Size:	150.5 KB
ID:	6284   Click image for larger version

Name:	apache16.jpg
Views:	71
Size:	243.6 KB
ID:	6285   Click image for larger version

Name:	apache 2.jpg
Views:	66
Size:	134.2 KB
ID:	6286   Click image for larger version

Name:	apache 6.jpg
Views:	76
Size:	111.2 KB
ID:	6287  
skipperdude is offline   Reply With Quote
Old 06-10-2011, 02:15 PM   #36
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 13,724
RE: Calculating hull speed.

Skipperdude,

Yes I see the pics. Still looks like a Tolly to me. And that ain't all bad as Tollycraft boats have a very strong following and are more efficient than their peers such as Uniflites*** ...mostly due to their narrower beam at the chines. Another efficiency issue for you could be weight. I see the bottom paint comes quite far up the topsides and I don't see it in the pics of the boat while underway. Mr Donald Jones may have built your boat a bit like my father had a lobster yacht built*** ....everything heavy duty to super heavy duty. The boat was so heavy it never did better than 9 knots w a 6-71 that had #80 injectors. I remember a farmer in Washington that built a home built aircraft but he used 2X4s instead of smaller Pisces of spruce. It never got off the ground. I see you've got a nice big rudder* ..very good. Does the marina facility there have a travel lift? Most of them (I think) have scales. Ask for a reading on the next lift. By the way the guy next to me in the harbor has a boat w a fuller bow and a bigger stern than yours. He has a DD 6-53 and tells me he runs the same speed as Willy but he's not concerned about economy as he runs his engine regularly at the dockside for hours. He also runs a sawmill and I think he's not happy unless he can hear big machinery running. I thought it had a very high idle speed but when a mechanic was there running his boat it was idling slower than I thought it could run.
Nomad Willy is offline   Reply With Quote
Old 06-10-2011, 03:37 PM   #37
Guru
 
skipperdude's Avatar
 
City: Whittier AK
Country: USA
Vessel Name: Apache II
Vessel Model: 1974 Donald Jones
Join Date: Oct 2007
Posts: 3,147
RE: Calculating hull speed.

She is kind of overbuilt. Mostly tractor parts such as huge ram cylinders for the steering and duel at that. Big rudder two hydraulic pumps one clutched the other a vickers constant for the steering. Not to mention the 3208.

SD

*
skipperdude is offline   Reply With Quote
Old 06-10-2011, 04:29 PM   #38
Guru
 
healhustler's Avatar
 
City: Longboat Key, FL
Country: USA
Vessel Name: Bucky
Vessel Model: Krogen Manatee 36 North Sea
Join Date: Oct 2009
Posts: 4,181
RE: Calculating hull speed.

Well, whatever it is, it's a really neat boat.
__________________

healhustler is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
What's your cruising speed. O C Diver General Discussion 282 11-14-2015 08:32 PM
Hull speed duckcaptainbill Marlow - Mainship 4 03-02-2012 12:08 AM
Your speed at idle markpierce Power Systems 34 10-28-2011 08:19 PM
calculating wiper arm and blade lengths? Daddyo Other Trawler Systems 3 07-18-2011 10:55 AM
Spray at Speed Marin Grand Banks 1 11-24-2008 12:32 PM




All times are GMT -5. The time now is 09:53 AM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2017, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012