Propeller Cage

[dwhatty]

Just finished installing one on our boat so we have to worry less about pot buoys. Had it made up locally of SS. For those of you who have never seen one, here's some photos. Hope it works out okay. Just have to remember not to back into a line or hit it with a log.

 

[FlyWright]

I like it!

 

[markpierce]

Do you have any concerns about rust if operating in salt water?

Electrolysis?: Will you be adding more zincs?

Will you need to remove the rudder to gain access to the propeller for its possible removal?

 

[Larry M]

Just finished installing one on our boat so we have to worry less about pot buoys. Had it made up locally of SS. For those of you who have never seen one, here's some photos. Hope it works out okay. Just have to remember not to back into a line or hit it with a log.

Looks great! Good design. How is the upper tab just forward of the rudder attached? And the bolts at the keel, thru bolted? Any surprises during the installation?

No more wrapped lines that's for sure. Please give us a report after some time in the water.

 

[dwhatty]

Do you have any concerns about rust if operating in salt water?

Electrolysis?: Will you be adding more zincs?

Will you need to remove the rudder to gain access to the propeller for its possible removal?

Mark:

Not concerned about rust. If in a few years it starts to get badly corroded, we'll have another made. This was not that expensive, especially relative to other boating costs.

Most of the fisherman do not add extra zincs or connect the cage to the bonding system (if they even have one).

Will see what it all looks like, including our usual zincs, when we haul the boat in 5 months or so and see if the zinc/bonding question needs to be re-visited.

It looks like I could just get the prop off and out of the cage w/o interference by the rudder. If I can't, I will just take one side or both sides of the cage off (it is made up of two pieces port and starboard) and the whole kit and kaboodle is designed to be removable.

I drilled and tapped the fiberglass of the keel for three 1/2"-20 bolts for the forward edges (on both port and starboard) of the cage. The glass was about 1 1/8" to 1 1/4" thick. The bolts tightened up nice and snug, but if they show any signs of not holding, will go to Plan B of through bolting using threaded rod (after we raise the boat from the bottom).

The aft end of the cage at the top of the hoop is bolted to a "T" fitting, which fitting in turn is through bolted with two 3/8-24 bolts up into the Lazarette and through a backing plate. The lower aft end of the cage is also fastened with a 1/2"-20 bolts on each side of the aft end of the skeg first into glass and then into about 1/2" of bronze that was inside the skeg. Am very confident in the aft end fastenings.

All holes and fastenings were well and thoroughly gooped with 3M 4200 (not 5200 thank you).

Two more photos showing the two pieces that make up the cage:

 

[Sailor of Fortune]

These prop cages are well regarded and a common add on in New England. They are common on Lobster Boats and a great addition to Non high speed yachts.

 

[SCOTTEDAVIS]

I not only like it, but it would fit on Firefly just fine.

hmmmmm

 

[Sailor of Fortune]

Firefly
Are you moored at Grand Harbor?

 

[Codger2]

Just finished installing one on our boat so we have to worry less about pot buoys.

WOW! can't wait to find out how it works, Dave! Are you in the water yet?

 

[Andy G]

At the risk of starting WW3, another potential benefit of a single screw boat?

 

[Peter B]

Andy...YOU CUT THAT OUT YOU NAUGHTY MAN...!

 

[SCOTTEDAVIS]

Firefly
Are you moored at Grand Harbor?

Yes

 

[Sailor of Fortune]

I saw your boat last fall. I delivered the Bertram 36 "Sweet Lelani" for my friend Steve. He has been at Grand Harbor Marina since Oct. He has a condo there, but lives in Philadelphia.

 

[Nick14]

A prop cage seems like a great idea and would be very helpful here on the Chesapeake where there are crab pots everywhere. Though the fishermen are not supposed to put them in many places, they routinely fill up navigational channels, entrances to harbors and marinas, wherever they think there might be a crab.

Does anyone have any experience with a cage regarding impact on speed? I imagine there would be a negligible impact on the performance of a full-displacement boat. Endurance is a semi-displacement design with a top speed of about 20 kts and a cruise of about 16-17 kts - I wonder what kind of impact a cage would have on that?

 

[Daddyo]

Can't be too bad as the lobstermen run those speeds and often have cages.

 

[Captain K]

One suggested change to consider on your next iteration of this excellent cage: Make the aft sides of the cage solid as they encircle the prop, thus creating a "duct" effect. I've seen those on large commercial vessels where they are said to offer a significant increase in propeller efficiency.

 

[Art]

David – Your SS two part prop-cage looks great and I feel your keel fastening system will last you well.

I've thought of cages on twin screw but very afraid to through-bolt into hull-bottom. Because... on our twin the cages would take the brunt of a grounding or deadhead collision... unlike yours having a skeged keel to greatly defer impact and also take the stress from fasteners. That is another good reason to like single screw boats! That said - For reasons, I'm still partial to twins!

1970... “Main Coast Shipbuilders”, Rockland/Owls Head (I then worked there at 18 yrs of age) had multi boat contract with Audubon Society for duplicate 31’ers. Each was being fitted with prop cage as Audubon planned to take their boats into real shallow waters (i.e. bird territory). These cages were through-bolted to the hull’s bottom (which I thought was risky at best if a deadhead was hit at speed or severe grounding occurred at speed). I heard the cages were no detriment to the speed of these fairly quick boats.

Main Coast Shipbuilders never did build all that were ordered due to its going broke as well as some real seamy business BS that its founder(s) pulled off. In my opinion that builder cut more corners in build-outs than a pizza maker shredding cheese! The two foremen reminded me of mafia types, big bad assholes providing shuck and jive!! My dad had been lead Purchasing Agent for that company and would tell me horror stories, he finally quit! Working there for a while I saw some real bad builds that were let fly! Dad and I knew the head guy from “Lang’s Boat Sales” and other boat yards in LI, NY. At about 15 yrs of age I was sitting in his LI office as this guy offered that (then future) job-position to dad... when we left – I said... dad, be careful, don’t trust him, that guy is a crook! In the long run I was proven correct!! He eventually (and suddenly) gutted Main Coast Shipbuilders of everything... then, from what I learned, he secretively fled to Canada.

 

[SCOTTEDAVIS]

I saw your boat last fall. I delivered the Bertram 36 "Sweet Lelani" for my friend Steve. He has been at Grand Harbor Marina since Oct. He has a condo there, but lives in Philadelphia.

That Bertram is a nice boat, I aim to miss it each time I return to my slip. :lol:

 

[dwhatty]

Can't be too bad as the lobstermen run those speeds and often have cages.

A knot or two for the fast boys is what I hear. Also, some that run that fast take an inch out of (or was it add an inch to) their prop pitch when they install a cage. I was told that at my speed (ha!) I needn't worry about that.

 

[dwhatty]

Dave! Are you in the water yet?

#@%*&#*@

 

[FF]

Can't be too bad as the lobstermen run those speeds and often have cages.

The cage is no harm at lobster trap working speeds , and the extra fuel burned at get home speeds , only a few percent of the work day.

 

[dwhatty]

Launched today and did the 3 1/2 hour run from the Yard to our home mooring.

Prop cage does not seem to affect speed. Same rpms give same speeds as previous years.

Ran over a couple of lobster pot buoys on purpose. Wife said I was tempting the Fates.

So far so good.

 

[Codger2]

Ran over a couple of lobster pot buoys on purpose. Wife said I was tempting the Fates.

I love it! :lol:

 

[FlyWright]

Now you can cruise in a straight line! Imagine the time and fuel savings!

In the words of Admiral David G. Farragut, "Damn the torpedoes! Full speed ahead!"

 

[SCOTTEDAVIS]

 

[dwhatty]

Now you can cruise in a straight line!

Am definitely looking forward to that, after all those years of leaving a wake that would break a snake's back.

Of course, most of the other boats around me will still be doing the lobster pot dance, which can get quite interesting in passing and intersecting situations involving multiple boats, including lobster boats hauling traps.

 

[Codger2]

Am definitely looking forward to that, after all those years of leaving a wake that would break a snake's back.

David: I'm trying to get my head around the concept of the cage and I understand it prevents trap lines from tangling in the prop. Won't trap lines still tangle on the rudder? ( I know that they are easily removed) I like the idea of not using cutters since they leave the whole trap (& lobsters) on the bottom, never to be recovered. What was your main incentive for building a cage? Prop entanglement? Saving the traps? etc.

 

[dwhatty]

David: I'm trying to get my head around the concept of the cage and I understand it prevents trap lines from tangling in the prop. Won't trap lines still tangle on the rudder? ( I know that they are easily removed) I like the idea of not using cutters since they leave the whole trap (& lobsters) on the bottom, never to be recovered. What was your main incentive for building a cage? Prop entanglement? Saving the traps? etc.

Walt:

Look again at the photos at the beginning of this thread.

The bottom end of our rudder shaft, unlike your spade type, is connected to the skeg. That in itself is somewhat helpful in avoiding snagging of a line on the rudder. (We used to catch lines too easily on our old boat that had twin spade rudders).

Also, the photos show that there is not much space between the aft end of the cage and the rudder. At any reasonable forward speed, the pot buoy (single or with toggle) is going to see something like photo 4 coming at it. By the time it (they) bounces off the bars we are gone by.

Catching a pot buoy and line (warp) while backing up, or having one insinuate itself in from the rear during a tide/current/wind shift while the boat is anchored or on a mooring, is something to be wary of.

My main reason for the cage was to avoid entanglement, which usually happens, and has happened to us, Murphy-like, at the worst possible time.

 

[Codger2]

The bottom end of our rudder shaft, unlike your spade type, is connected to the skeg.

Didnt realize that the IG 32 had a sand shoe. The whole reason for the spade (according to Harvey) was to result in a little more speed. Such, has not been the case with my boat but she does have a little different prop than you have. ( mine is 24.5 X 17.5)

 

[dwhatty]

Didnt realize that the IG 32 had a sand shoe. The whole reason for the spade (according to Harvey) was to result in a little more speed. Such, has not been the case with my boat but she does have a little different prop than you have. ( mine is 24.5 X 17.5)

Walt: Nice picture juxtaposition of two hulls that are essentially from the same mold but with different running gear and rudder treatment. Our prop is (back to, after a two year trial with a 24 X 20) a 25 X 19.