Proper Prop

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Outside of custom installations the only twin-engine production boat I'm aware of that puts a skeg-like keel in front of each prop and rudder as protection is the Great Harbor.
 
"the trick is going to be getting the prop off because they can jam themselves on pretty tightly."

Never had a problem when using*my prop puller. It works very well.
 
this gave more range? less fuel burn, enough to make a difference?






Marin wrote:Famous (and true) story about a GB42 owner who wanted to move his boat from Hawaii to the mainland under its own power.* He removed the prop from one shaft and went half the distance to the mainland on the other engine and prop.* At the halfway point he dove on the boat, removed the prop he'd been running on, installed the other prop on the other shaft, and ran the second half of the trip on the other engine and prop.
Click to expand...
 
Per wrote:

*
this gave more range? less fuel burn, enough to make a difference?


Marin wrote:Famous (and true) story about a GB42 owner who wanted to move his boat from Hawaii to the mainland under its own power.
Click to expand...
He ran on one engine for more range and removed the non-running prop to eliminate drag.* He switched props and engines at the halfway point so that both engines would have more or less the same amount of time on them at the end of the trip.* I have never heard if he carried additional fuel or not. I would have thought he'd have had to.* A GB42 can't come anywhere near to covering that distance on two engines and standard tankage and I would be surprised if it can do it on one engine and the standard tankage.

It was something of a stunt and nobody I've talked to on the GB forum thinks it was a smart or clever thing to do since a GB is totally unsuited for open ocean cruising.* Fortunately the weather cooperated for him.

*
 
markpierce wrote:

A properly designed, single-engined trawler should have a full keep to protect shaft, propeller, and rudder.*
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So, you would*not prepare for an unforeseen event that could possibly damage your prop,*like carrying a spare and gear/tools to change it?* You would rely solely on the design of the boat to avert a potential disaster?* Is this the common*practice among single engine/prop skippers?*** ***

*
 
KJ wrote:
You would rely solely on the design of the boat to avert a potential disaster?* Is this the common*practice among single engine/prop skippers?*** ***
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We don't run a single engine boat anymore--- well we do, if you count our outboard powered Arima fishing boat that cruises at about 30 mph--- but I think relying solely on the design of the boat is a foolish practice.* You have already seen some posts by the owners of single engine boats who had their props damaged.

As important if not more important than the design of the boat is the vigilance and skill of the person on the helm.* Given the staggering number of twin engine boats that are operated in the PNW, the number of running gear strikes is, I'm willing to bet, very low.* The secret to not damaging a boat is to not run into anything with it.* That doesn't happen because of the design, it happens because the person steering doesn't let it happen.* Or perhaps better wording is does everything possible to prevent it from happening.

Carey and his wife have a single-engine lobsterboat.* They run in the same water we do, often, if we're going to the same place together, on the same basic course we're following. They put every bit as much effort into spotting and avoiding logs, branches, lumber, crab-pot floats, kelp and eelgrass mats, and all the other crap we get in the water here as we do even though his boat's prop is protected by a keel and rudder shoe.* I think Carey has a spare prop for his boat at home, but he doesn't carry it on the boat.

The boat's just a tool.* How effectively and safely that tool gets used is up to the person using it.* Yes, sh*t happens, but there's a whole lot a person can do to minimize the chances of sh*t happening
smile.gif
* Relying on a keel and rudder shoe to keep you out of trouble is probably a pretty sure way of guaranteeing that someday, you'll get into trouble.

*
 
I thought I was about as vigilant as anybody out there but running up Clarence Strait we heard a big BOOOMMM. Neutral and idle as instantly as I could. Didn't fell anything that felt like a prop strike but it must have kissed it as we did feel a new but very slight increase on vibration. We saw the log 14" X 14' about. Could have sunk us. If we had had a twin it may have been more than a kiss. When hauled we found no marks.

The 36 GB has two 4JH Yanmars* 55hp each.
 
KJ wrote:

So, you would*not prepare for an unforeseen event that could possibly damage your prop,*like carrying a spare and gear/tools to change it?* You would rely solely on the design of the boat to avert a potential disaster?* Is this the common*practice among single engine/prop skippers?*** ***
Click to expand...
No I would not.* I've not the skills to install for example.* And if I was really worried, I wouldn't bother taking up boating.

*
 
Ken--- You seem very concerned about the various aspects of damaging running gear, the consequences, and what boaters do to deal with the consequences. I'm curious what prompts your concern. I'm not trying to imply it's nothing to be concerned about--- all of us, single engine or twin--- do everything we can to ensure we don't damage the running gear on our boats.

But I think Mark's answer above does a nice job of summing up the position most of us take. Most of us--- probably almost all of us---aren't experienced or qualified or fit enough to dive on our boats, let alone remove and replace a prop under water. So we simply operate in a manner that minimizes the risk. And I don't know any boaters myself who spend a lot of time worrying about it. Mark's answer in that regard was accurate, too. If the notion of running gear damage really caused me serious worry, I wouldn't have taken up boating. It's sort of like driving in a way. Two zillion people have accidents in cars every day. Does that prevent you from driving a car? If not, why not? And the proportion of boaters who have damaging running gear strikes is far less than the proportion of people who have car accidents.

So what concerns you the most about operating either a twin or single engine boat?
 
Marin wrote:

Ken--- You seem very concerned about the various aspects of damaging running gear, the consequences, and what boaters do to deal with the consequences. I'm curious what prompts your concern.*
*
So what concerns you the most about operating either a twin or single engine boat?
Click to expand...
Basically I'm trying to gather as much info/insight as to the*pros and cons of operating a single engine vessel as opposed to*one with*twins.*I've been focusing my boat search *primarily on twins as I believe that configuration would suit my needs best for the type of boating I plan on doing. However, the single engine folks have some valid, interesting rationales, very much worth looking into.* My concern with the damaged prop situation is that no matter how good your seamanship is, as you said "s**t happens".* It seems to me that sustaining a severe "hit" to the prop in a single engine*boat without the capability of effecting repairs could be potentially fatal to both vessel and crew (under extreme conditions). I am an accomplished scuba diver, but I don't know if I would have the ability to dive on my boat to replace a prop, even in a warm water environment.* My inquiry to single screw skippers is whether there*is an an overall accepted routine, drill, plan of action, or whatever you would call it, to prevent loss of your boat in*an extreme*situation.
It seems that there really isn't any, however,*it appears that*most skippers*don't worry about it that much after all.* I guess that's a good thing.***** KJ***

*


-- Edited by KJ on Thursday 17th of February 2011 12:31:03 AM
 
KJ wrote:My inquiry to single screw skippers was (is) whether there was an an overall accepted routine, drill, plan of action, or whatever you would call it, to prevent loss of your boat in such a situation.*
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While stuff happens, I doubt the number of single engine recreational boats, power or sail, that are lost as a result of running gear damage is very high.* Unless you are planning to boat in some very remote, rock and reef-strewn waters where you are well and truly on your own, most single engine boats that lose their means of propulsion end up finishing their run on the end of somebody's rope.* The plan of action I think usually calls for the use of the radio and some nervous waiting
smile.gif
*
 
Marin wrote:Unless you are planning to boat in some very remote, rock and reef-strewn waters where you are well and truly on your own*
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Actually, I do plan on operating in remote, reef strewn waters, quite on my own for extended periods of time.* The need to be able to effect repairs becomes a requirement.

*


*

-- Edited by KJ on Thursday 17th of February 2011 12:41:50 AM
 
So, do you think one keel-protected propeller and shaft*are*more vulnerable than two unprotected propellers/shafts?* In the nineteenth century, motor drives weren't well trusted so many ships had auxiliary sails.* Thus, if you don't have absolute confidence in your engines and propellers, shouldn't you have sails too?
 
Thus, if you don't have absolute confidence in your engines and propellers, shouldn't you have sails too?


Amazingly small sail rig works IF the vessel does not wish to sail with winds under 8-10K.

That's why they were called 50/50's.

Today with modern construction a 90/90 is quite easy to do.

The only real "compromise" is a bloat boat /roomaran cant be done.
 
KJ wrote:
Marin wrote:Unless you are planning to boat in some very remote, rock and reef-strewn waters where you are well and truly on your own* Actually, I do plan on operating in remote, reef strewn waters, quite on my own for extended periods of time.* The need to be able to effect repairs becomes a requirement.
-- Edited by KJ on Thursday 17th of February 2011 12:41:50 AM
Click to expand...
So where does the preparedness end?* Now I'm not saying don't be prepared but to what extent.* So you have a single or twin for that matter and you have some unforeseen item (dead head) jump up and hit your prop.* You dive down and see the bent prop but no worries you have a replacement.* You get your replacement on only to find out that the shaft bent as well. Now what?*

The point is that*you can not cover every thing that can happen.* Close in or far out.* I think that is why*most of us do not worry about it.* If you worried about everything that could cause an airplane to fall out of the sky you would only ride the train, then again there are all those things that happen to trains to worry about.

I'm not making light I'm pointing out that you are going to compromise.* Be it twins or*a single.*

*
 
KJ-* You say you are heading for the ends of the Earth - Where no one can come and help you.* You also say you are a scuba diver.* So I would bring a spare prop.

First practice changing it on land.

Then practice anchored in some calm spot and learn how to do it safely in the water.

You really may want to consider a full powered sailboat. I believe they have more long range capability than any trawler most people can afford.

For me prop damage is pretty low on my list of boating concerns.

Also towboat Us is just a phone call away.


As far as singles and twins go-- The best thing about singles besides the reduced operating, and maintance costs- is the room to service them-plenty of space all around the engine is really nice.

JohnP
 
A single engined trawler made into a twin engined trawler is fine as long as the total hp remains the same. A boat designed for 7 knots should have a different hull than one designed for 10 knots. If you double or half the power of a boat typical of TF boats the hull design should be changed as well. Unfortunately a whole lot of builders did the unprofessional mix and mismatch that resulted in the many undesirable combinations of hulls and engines. I posted a link to a GB36 that had been re-powered w 2* 55hp Yanmars. Unfortunately I think he should have modified the shape of his stern also. IF** ...the 36GB was properly powered w the single 120hp engine then GB should have offered 2* 60hp engines on the twin. IF the GB36 was properly powered w 2* 120hp engines then the single engined version should have had a 240hp engine. Boats are not like cars w a 100hp 6cyl offered in the same car as a 200hp 8cyl. Small boats like ours that go very slowly are (should be) designed for a fairly specific amount of power like 100 to 125hp. Or 200 to 240hp. The slower the boat the narrower the power band.
 
JohnP wrote:

KJ-* You say you are heading for the ends of the Earth - Where no one can come and help you.* You also say you are a scuba diver.* So I would bring a spare prop.

First practice changing it on land.

Then practice anchored in some calm spot and learn how to do it safely in the water.

You really may want to consider a full powered sailboat. I believe they have more long range capability than any trawler most people can afford.

**
JohnP
Click to expand...
Excellent suggestion, definitely will put that on my to do list.* While not exactly the ends of the Earth, as I said, I will be in some pretty remote areas (research), where self dependence becomes a necessity.*As Skipperdude says "if you can't repair it, maybe it shouldn't be on the boat".* A sailboat is not really an option for me, I will need the room that a trawler provides. Also,*although I will be travelling a good distance,*once*I get*there*I will be staying put for some time.* Again thanks for the tip, it's what*I was kinda looking for when* started this "conversation".**** KJ


*
 
nomadwilly wrote:

*IF** ...the 36GB was properly powered w the single 120hp engine then GB should have offered 2* 60hp engines on the twin
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Eric--- You keep missing the point with regards to GBs.**Because of the semi-planing hull, more and more buyers wanted to go faster when they wanted to go faster.* You keep assuming that*GB owners all*want to run their boats at displacement speeds only.* They don't.* We don't even do that*with our ancient '73 boat although we don't exceed displacement speed by much.* If GB owners all wanted to run at displacement speeds your statement*about one engnine of x-power or two engines of half-x power would be valid.*

But you are not taking into account*the desires of many GB owners, particularly those starting in the*mid 80s*on up to*today.* These guys want to be able to cruise at 14, 15, even 17 knot or more *if*they are in a hurry to get somewhere.** Yes, the fuel consumption goes through the roof but to these people the value of their time is worth far more than the cost of the fuel.* And American Marine/Grand Baniks understands what their customers want.* Hence the overpowered (by your philosophy) boats.* It doesn't work for you, but it works for the people who buy GBs.* Grand Banks would be foolish to ignore them.


-- Edited by Marin on Thursday 17th of February 2011 12:10:25 PM
 
KJ wrote:

*
Marin wrote:Unless you are planning to boat in some very remote, rock and reef-strewn waters where you are well and truly on your own*
Click to expand...
Actually, I do plan on operating in remote, reef strewn waters, quite on my own for extended periods of time.* The need to be able to effect repairs becomes a requirement.

*




-- Edited by KJ on Thursday 17th of February 2011 12:41:50 AM
*

my comment is two fold:

1. I am considering to take a divers course to be able to do some of these things, in an emergency or as general maintenance. I am now worried that even an experienced scuba diver is not able to do these things, please expand on this.

2. If you are concerned about loosing all propulsion you could make a device to mount a small o/b, certainly you will not be going fast, but it could assist to get you away from shore. My boat also comes with what appears to be emergency oars...


*
 
Per wrote:
Actually, I do plan on operating in remote, reef strewn waters, quite on my own for extended periods of time.* The need to be able to effect repairs becomes a requirement.

*
Click to expand...

1. I am considering to take a divers course to be able to do some of these things, in an emergency or as general maintenance. I am now worried that even an experienced scuba diver is not able to do these things, please expand on this.

2. If you are concerned about loosing all propulsion you could make a device to mount a small o/b, certainly you will not be going fast, but it could assist to get you away from shore. My boat also comes with what appears to be emergency oars...

The main comment I would make about changing a prop in the water is that you should try it before you rely on it. Changing a prop under water is probably ten times harder than doing so in the yard. Your body is trying to float this way and that, and never the way you want it to go. Your leverage is almost nil, given that you don't have your feet on the ground. If you drop the prop nut or cotter pin, or the prop itself, that puts an end to the process. I had my prop changed in the water once by a professional diver who does that kind of thing routinely. On my next trip out, I had made my way several hours north, and was just docking in Nanaimo, BC, Canada, and I gently hit reverse to stop my forward motion. When I did that, I heard a horrific thud, causing me to go straight to neutral, and jump to the dock throwing a line around a cleat to stop my motion. Once secured, I eased it into gear, only to find no movement whatsoever. The shaft being still in place, led me to the lack of a prop. I won't go into how it was allowed to fall off, other than to say it would not have happened if the previous prop change had been done out of the water.*

This event could not have turned out better, as we were able to get a diver to retrieve the prop just ten feet behind the boat within an hour of the incident. The same diver towed us to a yard the next day, where all was put right. Other than a small ding on one blade, and a ding on the shoe, it was all very minor.


We boat within easy reach of marinas, haulouts, Vessel Assist, and lots of friendly boaters willing to help, so I don't even carry my spare prop. I keep it at home in case I need to take my primary prop to the shop. In fifteen years, the worst damage done to our prop has been a quarter inch ding from a small stick I didn't see.


Final note. Even if you don't get my prior points, or think yourself able to overcome all of the above, consider what would happen if a passing boat wake caused your boat to lurch and come crashing down on your head while attending to the prop.




*




-- Edited by Carey on Thursday 17th of February 2011 12:42:56 PM
 
Marin wrote:
"Eric--- You keep missing the point with regards to GBs."
You're the one "missing the point" Marin. Semi-planing boats are fine but it's up to the operator to operate them responsibly. The old 36 and 42' GBs w single engines are the ones that are improper designs**** ...disp power w semi-displacement hull. Marin you keep missing that point. The single engined boats needed a different hull having nothing at all to do w the number engines they have but all to do w the power they are equipped with.
 
When we cruised across the pacific under sail we changed the 3 blade "motoring" prop to a 2 blade that had much less drag under sail. When we got the the Tuamotus I anchored in sand to the point the keel touched, then ran out a stern hook and snugged the boat tight. I donned every bit of weight we had and threw the 3 blade over the side and jumped in with scuba gear and in tennis shoes. I sunk to the bottom like a stone and changed out the two props. Even with the right tools and having done this a bunch of times on the hard it still was a real chore., and I never had any issues with the install afterwards.* If I wasn't able to set stuff in the sand, and get a better purchase by having my feet on the bottom it would have been really difficult
And this was a small prop on a 30 hp sailboat... impossible to do it solo with a prop the size on Volunteer
HOLLYWOOD
 
nomadwilly wrote:The single engined boats needed a different hull having nothing at all to do w the number engines they have but all to do w the power they are equipped with.
Click to expand...
According to American Marine's own literature they chose the hard-chine hull (they did not refer to it back then as either semi-displacement or semi-planing) because of the stability of the ride if provides.* They then selected the best engine that they felt was available to power the thing which was the FL120.* The Cummins 210 which went into a lot of later GB36s wasn't available then.* Neither was the Lugger 150.* Or the larger Cats*and John Deere's*that*were used in*1990s on.* But even from the outset, AM promoting their boats as having a degree of speed for this type of boat.* Take a look at the promotional photos of Spray sometime.**They're*moving it along at a pretty good clip.*

Nowhere did AM promote their GB-line as displacement-speed boats.* The phrase they used was "Dependable Diesel Cruisers."* And single-engine GB42s were not very common.* Most buyers wanted twin engines, even if*all they were were FL120s.*

So I think what you believe AM should have done is not what their customers wanted them to do, even back in the late 60s and early 70s.
 
I give up. You just don't get it Marin.
 
Thanks Mike,
It may have been a good move but I'll never know since you deleted it.
If Marin gets it he's pretending he dosn't.
"no mater how I write about Eric and his understanding of yacht design it comes out as a personal attack."
Is the personal pronoun in this sentence you or Marin?
But if you can't talk to me without a personal attack let's drop it.
And I'm through trying to reason w Marin.
 
nomadwilly wrote:

Thanks Mike,
It may have been a good move but I'll never know since you deleted it.
If Marin gets it he's pretending he dosn't.
"no mater how I write about Eric and his understanding of yacht design it comes out as a personal attack."
Is the personal pronoun in this sentence you or Marin?
But if you can't talk to me without a personal attack let's drop it.
And I'm through trying to reason w Marin.
Click to expand...
Forgive me for butting in, but if I'm not mistaken, Mike was saying that Marin gets it, and you don't. Just my humble interpretation. Hand me the big spoon and I'll stir a little more.*
no.gif


*
 
nomadwilly wrote:

Thanks Mike,
It may have been a good move but I'll never know since you deleted it.
If Marin gets it he's pretending he dosn't.
*And I'm through trying to reason w Marin.
Click to expand...
Forgive me for butting in, but if I'm not mistaken, Mike was saying that Marin gets it, and you don't. Just my humble interpretation. Hand me the big spoon and I'll stir a little more.*
no.gif


*

Geez guys, this is really so much fun!* You would never guess that you guys are friends.* Can either of you explain to me what you are so contemptuously bashing each other about ?* I seem to have lost the content of your original point.* I was asking for advice about props, not an argument over naval architecture.*
A lot of folks on this forum consider you guys as a major source of valuable info, but you diminish your stature when you go after each other. It's like you begrudgingly divulge your knowledge.* But hey, that's just me.* I've already gotten some good advice from a bunch of folks,*so maybe this would be a good time to put this thread to bed*(hey, that rhymes).**Thanks every one for a great response.***** KJ*

ps I 'm gonna catch hell for this one, ain't I?*


*

-- Edited by KJ on Friday 18th of February 2011 03:48:45 AM
 
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