Speed difference between Port and starboard tack

[sleather]

Promotion!

This is going to yet again illustrate my novice status but today I went for a beautiful sail on Lake Ontario.

Your "novice status" has been upgraded! The fact that you "noticed" and were "concerned" about a relatively minor item that would escape the attention of the "average" recreational sailor is a good indication that your progressing up the "learning curve"!

 

[Dave Hussey]

I hope that the problem is solved. When sailing my E27 this summer, I thought I was either hallucinating, or my boat favored one tack over another. This is still inconclusive, but after reading this thread, I have a better defense. One thought that comes to mind regarding my boat at least, is the starboard offset of the shaft and propellor. I've recently installed a 12 inch diameter 3 blade Michigan prop and I'm wondering if it is acting like a drogue on one tack, and hidden behind the keel on the other tack. Or, I'm just hallucinating....

 

[sleather]

One thought that comes to mind regarding my boat at least, is the starboard offset of the shaft and propellor. I've recently installed a 12 inch diameter 3 blade Michigan prop and I'm wondering if it is acting like a drogue on one tack, and hidden behind the keel on the other tack. Or, I'm just hallucinating....

Could be, the shaft & prop would be exposed on one tack, and in the "shadow" of the keel on the other.

 

[msc1212]

Propellor

Out of curiousity, do you keep your propellor engaged when you sail or in neutral so it can freely rotate while sailing?

Michael

 

[Seth]

That will be some of it

You seem to have found part of the problem-if there is one. Of course-take the advice here to make sure you do not have structural problems, then tune the rig centered in the boat and straight side to side. Set prebend to match you mainsail (lots of posts on this here), and as you already know, make sure you set the boat up the same way on each tack (trim, heel, etc.).

If you have a knotmeter, and it is on centerline, it will give more meaningful tuning info than a GPS. If the transducer is off to one side, or not very good, use the GPS-sounds like you understand the variables-but GPS is not the way to tune a boat in general-too slow to respond (many of them anyway), and is not giving you what you want. It gives groundspeed and direction over the ground, not boatspeed or heading..But if that is what you have, so be it.

Again-if the rig is off more than an inch to one side, you will notice the clew of the headsail higher off the deck on one tack than the other-when trimmed in the same amount of course. You can use a mark on each genoa sheet measured at the same distance from the clew, and see where it is reference something fixed-like the cabin top edge, a winch, turning block, etc. If the marks are the same on each sheet, and they line up with whatever marker you use on each tack, you have it trimmed the same amount on each tack.

Then you can see if the clew is higher on one side you can confirm if the rig is off to one side or not (a double check against the rig measurements you are aready doing)...

BTW-It is best (unless you have a hydraulic tranny) to leave the prop in reverse while sailing. Leaving it spinning slows you down, and even worse, the tranny has no lubrication if the engine is not running, so the shaft is spinning away without being lubricated. Lock the prop.

If you have a 2 blade, when you are the dock, dive down and with the engine in neutral, rotate the shaft until the blades are straight up and down-then using a magic marker, nail polish or tape, mark the top of the shaft near the coupling (somewhere where you can see it). When you will be sailing for any period of time, shut the engine down, put it in reverse to stop the spinning, then neutral again so you can reach down and rotate the shaft to the vertical, marked position, then engage reverse again to lock it. This will reduce drag considerably and help sailing speed! We do this all the time with folding props, but the mark indicates the blades are horizontal, not vertical, so they fold back and cannot "drop a blade" if you slow down...

Good luck!

S

 

[Frank Langer]

Seth, are you sure....?

Seth, on a folding prop, shouldn't the blades be vertical rather than horizontal to avoid them falling down--as in your post above? If horizontal is correct, I'm puzzled. I have a folding prop, so this is of interest, though my Varifold 2-blade is geared, and I understand they are less likely to have one blade drop.
Thanks,
Frank.

 

[Seth]

It depends

On the definition of vertical, I guess. The 2 blade fixed should have the blades straight up and down, but the folding prop (as you say) must be rotated so the blades cannot fall down-that means they would open side to side, which to me is horizontal..Either way it is opposite of how you would lock a 2 blade fixed prop..

Does that make sense? Now you have ME confused!!

Cheers,
S

 

[Frank Langer]

ok, it does get complicated quickly...

Seth, I think we are in agreement that when closed, the blades on the folding prop need to be straight up/down (vertical to me) rather than flat (horizontal to me), so that they would open to the side rather than falling down if the boat slows.
It makes intuitive sense, but trying to put words to it is not so easy.
Frank.

 

[obiwanrazzy]

Ya learn something every day

...BTW-It is best (unless you have a hydraulic tranny) to leave the prop in reverse while sailing. Leaving it spinning slows you down, and even worse, the tranny has no lubrication if the engine is not running, so the shaft is spinning away without being lubricated. Lock the prop...
S

For real? The spinning prop slowing the boat down more than fixed *seems* counter intuitive. I'll take your word for it, however. Your point about tranny lubrication is something that never occured to me tho. Makes sense...

Ya learn something every day. Thanks.

 

[Seth]

You are correct Frank

Good to be back on the same page, eh?
And yep-a spinning prop creates a flat disk the size of the prop diameter-which is a lot of drag. Lock a 2 blade (for example) vertically and it sits right behind the keel, presenting MUCH less area to the H2O...

S

 

[Dave Hussey]

...locked in reverse is better...I didnt know that. I dont think my shaft is turning when I'm sailing, even though I keep the drive in neutral, but I will try reverse to secure it. With a three blade I wonder if I should keep one blade at 12 oclock, so the other two are symmetrically at 4 oclock and 8 oclock????

 

[Emerald]

...locked in reverse is better...I didnt know that. I dont think my shaft is turning when I'm sailing, even though I keep the drive in neutral, but I will try reverse to secure it. With a three blade I wonder if I should keep one blade at 12 oclock, so the other two are symmetrically at 4 oclock and 8 oclock????

Hi,

I believe the locking in reverse really is more of a Yanmar cone type transmission issue. If put in to forward, these guys can get stuck in gear from the loading created by the prop, but in reverse they're OK.

I have a 3 blade prop and have often wondered what it's ideal position is. By nothing other than seat of the pants and what sounds good over a cold beer, I go for one blade straight down behind the keel and the other two making a "V" that hopefully gets some help from being sorta like the shape of the hull. I keep meaning to try to test this, but find there are too many real life variables and other basics like keeping the sails at optimum trim that make more difference more of the time

 

[Loren Beach]

Ericson used (mostly) Universal diesels. Universal usually provided a Hurth transmission. My Universal manual specifies that the trans be left in "reverse" while sailing. Prevents rotation without harming the transmission, from what I understand.
We have to lock it, anyway, so that the blades on the feathering prop will allign.

Loren

 

[NateHanson]

For real? The spinning prop slowing the boat down more than fixed *seems* counter intuitive. I'll take your word for it, however. Your point about tranny lubrication is something that never occured to me tho. Makes sense...

Ya learn something every day. Thanks.

Have you heard of helicoptor rotors with stalled engines being used to "auto-rotate" for a softer crash landing? The idea is that you allow the prop to freely rotate because it provides much more resistance than a stopped rotor. Also, an auto gyro generates lift by letting an overhead rotor spin (unpowered) as another prop pushes the craft forward.

 

[Shaggy]

You know, I thought I was crazy, too...

I noticed a similar speed differential between tacks and thought maybe it was the angle of the swell, or something. I also couldnt point quite as high on port tack.

After reading this thread I scrambled to the base of the mast while close-hauled, and yes, my rig is out of tune!!

All is straight and true in the slip with no load on the rig, and the chainplates are all solid. I did notice the leeward shrouds were a bit slack while close-hauled.

Thank goodness for this thread! Glad to learn, and kind of discomforting to think I had been sailing in some pretty stiff breezes (25-30 knots) with such a large rig out of whack!!

More newbie learning....

BTW, the Ericson owner's manual for my E38 also mentions locking the transmission into reverse while sailing.

 

[NateHanson]

Take a look at a book for info on tuning your rig from start to finish. Every sailor should know how to do this, as it's not very hard to do a basic job, and it's really essential. (I don't mean to say that any dumb sailor can do a real professional race-tuning like a rigger, I'm just referring to the basics required to keep the mast up, and the boat sailing, which I think is within anyone's capabilities.)

I first learned tuning from Ferenc Mate's "Shipshape", but I'm sure there are many other (more modern) tuning lessons out there in other books.

 

[Frank Langer]

Nate,...

Nate,
You're right that rig tuning is an essential skill for sailors, but I don't agree that it's pretty easy to learn from books depending on the boat. I had it down to a fine art on my previous boat, a single spreader, mast head sloop. With a Loos gauge, knowing the breaking/working loads of shrouds of various diameters, and understanding impact of backstay adjusters, etc., I got pretty good at it.

Now that I own an E30+ with fractional rig, double spreaders and cap, intermediate and lower shrouds, it's not so straight-forward. The one-pager from the manual (included in the documents section on this site) is not very helpful--uses terms like make the cap shroud "firm" and the lowers slightly less so, and avoid having the lee shrouds loose but don't overtighten so as to stress the hull--ie. all so subjective and general as to be unhelpful in my opinion. Books like Brian Toss' Rigger's Apprentice also only include general information (only about a page on the actual tuning).

I have done a full search on this site (and others, like Sailnet) on rigging and while there are lots of posts, they tend to lack specific information. Most indicate that as long as the distance from mast top to chainplate is equal on both sides, the mast is straight, and does not fall off to leeward in a moderate breeze, that's good enough. But in my opinion, that still leaves alot of room for error.

In fairness, I know that each boat will be a bit different, and tuning varies a bit depending on sailing conditions. But I can certainly understand why there are a number of boats out there that are not tuned well.

If anyone knows of a good book or website that provides detailed information (with specifics on amount of shroud tension, relationship between tension of the cap, intermediate and lower shrouds, backstay, etc.) on rigging a fractional 2-spreader boat, I'd sure like to hear about it. I am still fine-tuning adjustments on our boat after our first year of sailing to get it "just right" and can still use any advice.

Frank.

 

[sleather]

Rocket Science

Frank, I think what Nates refering to, is that every sailor should attempt to understand the "basics" of a simple rig, and be "aware" of what's going on with their boat. Rigging 101, simple tuning is not "rocket science"!

The Rig you describe is a very complicated arrangment and beyond the ability or desire of the average sailor to understand themselves(that's what the PRO's are for)!

 

[Seth]

rig tune

I think there are some very detailed posts on this site giving step by step methods for tuning rigs-which will cover your 30+..If nothing else they are a fairly good starting point (I think)..
S

 

[Frank Langer]

Steve,
Maybe you're right, that we should all understand simple rig tuning and use the pros/experts for the rest. But while I do use professionals for some work on my boat (eg. diesel engine work, some electrical, etc.) I think with reasonable care, it's possible to do a satisfactory job of tuning a double spreader fractional rig (a number of the Ericsons have similar rigs).

I have come across useful figures on shroud tension for masthead rigs (eg. up to 20% of breaking strength for outer shrouds, 12 - 15% for inner/lower shrouds). But similar information just doesn't seem to be available for double spreader, fractional rigs--and yet, the principles are similar.

While Seth is right that there are some useful posts on this site, I have yet to come across any that state what the cap shroud tension should be (other than firm, with straight mast and no looseness--too general, in my opinion) or just how much looser the lower shrouds should be than the upper, etc. While the basic concepts of straight mast, avoidance of sloppy/loose shrouds, weather/lee helm are all good, for those of us who want to sail our boats to their potential and avoid unnecessary stress on the rig/hull, I still maintain that good detailed information is very hard to find.

I am hoping someone can prove me wrong, but meanwhile, I'll continue to read as much as I can and talk with other sailors, and experiment on my own. And I'll continue to enjoy the way our boat sails.

Frank.