Wonderful non-parallel shafts

[Captain Ray]

In 2012, had a cracked engine block on my 76, F30 with straight shafts and it steered well while only using the remaining engine. At a previous time, I was aboard a friends "Bertram 28 II", when one engine failed. We had a hard time getting back to his slip - it would only steer in circles. We had to hang three five gallon buckets over the one side to travel a straight course. While searching for an explanation, I found the following when looking at the hulls:

The Bertram propellers, when measured from the hull centerline, were wider than the engine fronts - in other words, shafts toed out.
My Trojan is oriented opposite, with the propellers narrower than the engine fronts - in other words, shafts toed in. The combined thrust is noticeably different in these two cases.

So, now, when asked how I can operate/steer with only one engine, I explain it by describing the "non-parallel shafts" design.

This was a nice surprise as I know I can operate on one engine in case of an engine casualty. It also works well to operate on one engine to save fuel when in no particular hurry. Some boats cannot do this!

Naturally, during close maneuvering the "back and fill method" is used to steer. And, one cannot plane the hull with only one engine.

The above is an example of why it is nice to own a Trojan!

What is your experience?

Ray

[297Elegante]

On one engine my Silverton 34C tends to go in circles. Unsure on shafts verse engine orientation though.

[prowlersfish]

The B28 also has very small rudders ( along with the B31) Many have been refitted with larger rudders

[Captain Ray]

The moral of the story here might be - know your boat - and if you need to carry a drogue or two, buckets or whatever, it is fun to find out before you are stranded. The hourly towing rate here on southern Lake Michigan is $225/hour, portal to portal. Remember Murphy's Law! The friends Bertram lost engine due to ethanol effect on his fiberglass gas tanks - plastic resin dissolved into gas.(Only a few manufacturers used FG for gas tanks)

I have always thought the rudders on recreational power boats look too small - the sweet spot for size is likely related to hull speed -faster boat, too much drag with large rudders. Sailboats do well with huge rudders but they operate at "hull speed".

[aaronbocknek]

nice to know and great information. now, do all trojans have toed in shafts/props? how did you discover the orientation, engine vs props? when i take ENTERPRISE out for her first spin of the season, should i try the one engine method? i'm curious to see how the tri cabin will operate on one screw. and, is it best to try p vs s and vice versa?

[Captain Ray]

I cannot answer whether all Trojans are designed this way, but looking at mine, it definitely was designed this way for a purpose. I can see the proof in pictures taken in 2005 and 2006, when doing demolition and reconstruction. I did not think anything about it until the Bertram experience. I was then able to test my theory when I had the bad engine last July.

From the inside of the hull, the non-parallel is clearly visible. In the first link below, look at the position of the rudder posts and the rectangular plywood blocks which backed up the shaft hangers - the angle is visible. In the second picture link the humps for the shaft penetration also show the angle. The orientation is a little harder to see from the bottom of the hull, but can be measured.
http://www.flickr.com/photos/34406277@N04/8644709401/
http://www.flickr.com/photos/34406277@N04/8645818270/

Just guessing, Trojan may have started building shafts this way early on when building wooden hulls, but have no information if all models used this idea, especially when they introduced the Deltaconic hull shape.

I would recommend experimenting with your boat and then create an emergency backup to have in case of an engine casualty. The other thing that might be important on your boat is the transmissions - I have velvet drives and the owners manual states that these internally lubricate without the engine running, so it is fine to let the shaft freewheel. I have read that some transmission brands require a shaft lock if freewheeling for a long time(also happens in current while anchored).

Hope this helps!

Captain Ray

[Commissionpoint]

I run single screw a lot. Fishing mostly, but sometimes I am just being cheap.

I can run on the Stbd. down to about a stall and still have steering control, albeit reduced. Its not as easy on the Port side but still possible. I suspect something to do with direction of rotation and pitch.

[Captain Ray]

Mine steers the same, either one engine or the other. Everything is symmetrical - rotation opposite dir. Steers well manually or when using auto-pilot. There is about 7 degree correction to go straight when engine out of gear or off.

Captain Ray

[P-Dogg]

when i take ENTERPRISE out for her first spin of the season

What you haven't been out yet? Shed the slip queen image (talking about the boat, Aaron) and get out and see what she does on one wheel. Aren't you in the middle of 13 days between shifts? Last year you had an excuse. Time to make up for it.

Ah yes, the post...

The Bertram propellers, when measured from the hull centerline, were wider than the engine fronts - in other words, shafts toed out.

Over the winter, after my knuckles were too bloodied from being scaped against various parts of the bilge to pick up another cold wrench, I read the "Boat Mechanical Systems Handbook." It mentioned that boat designers can squeeze an extra inch or two of headroom above (or for) the engines by biasing them toward the center relative to their respective screw (toe out). This is because of the vee shape of the hull. There is just more headroom at the keel than at the chines. As for toe in, the book said that permitted a narrower stern.

A friend of mine had a 38 ft Bertram. The rudders were TINY -- I think because the boat was meant to run WOT with plenty of propwash over them out to the fishing grounds , not dawdle around. Stern quartering seas were always fun.

[aaronbocknek]

when i take ENTERPRISE out for her first spin of the season

What you haven't been out yet? Shed the slip queen image (talking about the boat, Aaron) and get out and see what she does on one wheel. Aren't you in the middle of 13 days between shifts? Last year you had an excuse. Time to make up for it.

shifts? good grief.... trips or pairings or sequences, but certainly NOT shifts. and some of my time off is peppered with endless doctor visits, sometimes, on lab and physio days, it can last most of the day at hopkins.

no perry, i have not been out of the slip yet. #1. it's been way too windy for me to even attempt to handle her alone, and #2 my canvas man just called me yesterday (the 13th) to inform me that my top and aft drop were ready from being restitched. trying to take her out with the winter cover on the bridge would not work, and the canvas frame is laying on the bridge deck so access and mobility are greatly impaired--- i.e. unsafe for foot traffic. with my lack of balance sometimes (thank you very much chemo therapy) i do not feel as sure footed as i once did. have no fear though, she will leave the dock this spring and i fully intend to try the one engine gig. i'd like to know how she handles that way. btw... your 'new slip' is begging for you. mike and i heard it call out to you!!! i see that you are going to be neighbors with greg and mary. nothing like having a 3 story chris craft right next to you!!! didn't you inspect their tri cabin when you were looking around?

mike and i are looking forward to having you as part of the parkside trojan gang.

[prowlersfish]

Aaron , I thought you knew how it handled on one ? Didn't run it on one because of the bent prop ?


As far as handling on one ,rudder size has a lot to do with it .

[75 Tri Cabin]

My Tri Cabin steered quite good on one. I still have a blown tranny and something wrong with the vdrive. I think the v drive problem is the key on the input shaft. Don't have time for the boat with the wife and her lung cancer. Got down there yesterday and hosed off all the pollen on the boat. What a mess.

[aaronbocknek]

Aaron , I thought you knew how it handled on one ? Didn't run it on one because of the bent prop ?


As far as handling on one ,rudder size has a lot to do with it .

the port prop was bent yes, but was turning at just below 900 rpm so as not to create vibration above that speed. in fact, when jerry and i took her to sue island for her haulout, we only cruised at that speed. but, all things being equal, she handled okay with 'one'. no spinning around in circles if that's what you mean. she actually tracked fairly true with minimal intervention with the wheel. then again, the conditions were very light winds and calm waters.

[gettaway]

I ran from about 3 hours from Marina Del Rey to Two Harbors Catalina on the port engine when I brought the Silverton 37 down a month ago (anti siphon valve problem) and the boat steered straight as an arrow. The boat has big props, 23-1/2" X 23" and they are fairly far apart, the boat also has nice big rudders, if you look at the photos below, the props are 23" you can get an idea of the rudder size if you compare them to the props.

[Commissionpoint]

Yeh, thats good sized running gear for sure Scott. Looks good though.

I have 15x16's and those tiny stock F-32 rudders. I haven't measured, but I would imagine there is room for 17's on the Trojan.