Paravanes boom position?

[Cold-smoked]

Hi, all. I've been reading some of the threads here regarding paravane stabilizers with great interest. It seems that most boats have the booms installed near cg(?) - or around 1/3 of the boats length from the stern.

What exactly are the negative effects of having the booms and vanes closer to the bow - apart from perhaps reduced rudder response ?

I'm asking because I found pics and illustrations of boats where the booms are closer to the bow - and also because I plan to dampen the roll on my own former FV. The easiest for me would be to install the booms near the front mast, but I realize it may not work so well




Thanks, V.

 

[Lepke]

My fishing boat (55') had the poles about 1/3 of the boat length back from the bow. I've seen them rigged everywhere between the 1st 1/3 to the last 1/3 of the boat. The poles should be fine where they are in the picture. The angle when out was about 45°. I used a commercial paravane similar to the picture.
If you're going to cruise with them in the water, use a hole forward of center. I only used mine when trolling or anchored, so used a hole toward the back that also slowed me down to trolling speed. Rigging needs to be stout. The poles aren't just lowered, they're locked in position. I had brackets on the pole and mast that held a stout wood brace when in position. The pole was lowered, a little too far, the brace inserted into the brackets and the the pole pulled up until the brace was locked in position. Some people had an eye bolt near the waterline and used that to hold down the pole.
In the ocean, 45° seems to work well although I had my poles in the water a few times. Pics - one poles forward and one poles aft. Both line up with the mast. 2nd boat has the poles off, but the bracket is on the rail. Doesn't really make a difference where the poles are.

 

[AusCan]

Welcome to the forum, Cold-Smoked. Its nice to have a Norwegian on board. Both myself and my boat are of Norwegian heritage.

Sorry but I don't have much experience with paravanes, but I'm interested in learning more so I'll be watching this thread.

 

[Cold-smoked]

Thanks, Lepke and AusCan - I appreciate it.

Bilge keels are what is commonly used up here, but not very effective from what I 've heard. So what I know about paravanes, is what I've read here.

Regarding the position of the poles, I believe someone here referred to Beebe's book - saying that ~28% from the stern is the best location. I can only imagine that this has to do with rudder control, I guess the effect is similar to that of daggerboards location on a sailboat. Also, I think it's possible that the boat will be pulled a bit down by the vanes when going over wave tops -if the poles are too far from CG.

My boats front mast is around 1/3 length from the bow, would be great if that works.


Thanks, V.

 

[JDCAVE]

We have found that when the seas get more extreme, the autopilot has more difficulty maintaining course when the paravanes are in the water. This has happened on a couple of occassions and I had to reset the AP. I think you might find that the vessel will hunt more if the forces are too far forward. It’s a good idea to consult with a naval architect prior to installation. I am aware of a couple of cases where the install failed when in use on KK42’s.

 

[McGillicuddy]

CS, interesting topic.
Dragging paravanes causes drag which is resistance. To overcome resistance requires effort.
The center of effort is not at the paravanes as most people would think. Nor is it on the outrigger poles. It travels through the rigging and ends up being at the head of the mast that supports the poles. This is a fixed position and cannot change.
The net effect is to raise the vertical center of gravity (VCG) which will in turn reduce the righting moment (GM). Because the masthead is high above the vessel center of gravity (G), a small amount of force (resistance) has a large effect because the moment is calculated as force x distance. So the relatively low resistance is multiplied, causing a disproportionate affect on intact stability, reducing the righting moment and slowing the roll period.
Concurrently, the position of the mast horizontally affects the position of the longitudinal center of gravity (LCG). In your case, it will move it forward. Again, this a moment calculated as f x d. Force remains as resistance. Distance in this case is the distance from the vessels original LCG to the mast base. That lever would be applied to the overall calculation of the position of the LCG in a total moments calculation and the net effect will be to move the LCG forward, but not as much as you might think.
The vessel rotates or turns around the LCG. Pushing it forward INCREASES the distance from the rudder post so the effect the rudder makes on turning INCREASES, again due to the turning moment is f x d where f=rudder force. Some people may consider that this new steering effect makes the boat squirrelly.

In your case, the boat was designed to drag nets which have much more resistance than the paravanes might make. My opinion is this will be a non issue. If you have any real doubts, you can consult a naval architect to make a calculation using real numbers.
Best of luck with your boat. We would all love to see some more pics and details.

 

[JDCAVE]

McGillicuddy describes some the forces more eloquently than I did.

CS, interesting topic.
Dragging paravanes causes drag which is resistance. To overcome resistance requires effort.
The center of effort is not at the paravanes as most people would think. Nor is it on the outrigger poles. It travels through the rigging and ends up being at the head of the mast that supports the poles...

...but also to the bow of the boat through the forestays on either side, which will serve to apply rotational forces at the bow. At least I think it does. And that force may not be even (port and starboard) through the wave period if the direction of travel is at angles to the beam sea.

Be aware that the forces are considerable and failure of the system typically comes when you need it the most. Some people tend to underestimate the forces on the rigging and under-build their setup. Don't make that mistake. Also, it's important to replace the stays regularly. It's cheap to do so (perhaps $200-300 for the 4 stays). The consequences of rigging failure are considerably more expensive.

The position of your mast can't be changed and you might be challenged by that. I think the best advice is to consult with a naval architect. I know of instances where people have relied solely on the advice of fabricators who are less familiar with the forces involved and the systems failed.

Jim

 

[McGillicuddy]

McGillicuddy describes some the forces more eloquently than I did.



“...but also to the bow of the boat through the forestays on either side, which will serve to apply rotational forces at the bow. At least I think it does. And that force may not be even (port and starboard) through the wave period if the direction of travel is at angles to the beam sea.”



Sorry Jim, that’s not quite right. Its the opposite, stays do dissipate the stress on the head of the mast but don’t do anything to move the center of effort.

 

[Larry M]

This is from Beebe's first edition (1975). It gives you an idea of the loading for paravanes. He's was convinced that the fish can generate resisting forces up to 10 lbs. per square inch. Our fish are ~220 square inches each. Proper design is critical.

 

[JDCAVE]

McGillicuddy describes some the forces more eloquently than I did.



“...but also to the bow of the boat through the forestays on either side, which will serve to apply rotational forces at the bow. At least I think it does. And that force may not be even (port and starboard) through the wave period if the direction of travel is at angles to the beam sea.”



Sorry Jim, that’s not quite right. Its the opposite, stays do dissipate the stress on the head of the mast but don’t do anything to move the center of effort.

Perhaps I’m missing something. It’s still somewhat logical to me there would be a rotational force about the mast, exerted on the tip of the boom by the forestay. Pardon my schematic drawing of a birdseye view of a vessel with paravanes in the water. If you only had the port side paravane in the water, would there not be a rotational torque to port?

 

[JDCAVE]

Another photo of the attachment of stays to the tip of the boom.

 

[chriscritchett]

Perhaps I’m missing something. It’s still somewhat logical to me there would be a rotational force about the mast, exerted on the tip of the boom by the forestay. Pardon my schematic drawing of a birdseye view of a vessel with paravanes in the water. If you only had the port side paravane in the water, would there not be a rotational torque to port?
View attachment 72716

Actually a plenty good diagram. But the forestay only resists the load pulling aft on the pole. The net effect on the boat will be that aft pull x distance off C/L, centered around the mast location (just like the diagram shows). The forestays could lead anywhere forward; doesn’t really matter.

With 2 fish pulling aft equally, no net effect on steering. But since the drag is a component of the total pull from the fish, it’s rarely going to be even from side to side; there will be some effect on steering forces. Also, don’t forget the downward pull. That’s acting thru the mast location as well. That’s going to have an effect on pitching.

Will it work to stabilize against rolling if it’s forward? Sure. But what seems to have been true on Beebe’s boats and many others is that the typical center of motion overall is ~1/4 - 1/3 of the LWL forward of the stern. If you center the mast & stabilizer forces at that location, you won’t change much except the rolling motion. If you move the stabilizer forces forward or aft, you’re going to change something - pitching and / or yawing motions - and that will almost surely increase resistance and maybe make the steering ‘squirrelly’. Even assuming the rudder can counteract it, it’s creating more drag in doing so.

Now all that said, an NA much more familiar with your particular type of boat should have some valuable input. The comments about dragging fishing gear from there are quite valid, but remember that fishing may not have been done at your cruising speed. And Beebe was hunting for the ‘best’ location; the difference between that best and your actual location may not be a big deal. Giving up an extra fraction of a knot to get stabilization vs not having any is an option many would enjoy having.

 

[Diesel Duck]

From my memory, the location for the paravane poles is to mount them 27% forward of the stern, using LWL as your 100% number.

.

 

[Cold-smoked]

Thank you guys, all good and useful information.

I have decided to give it a try, and install the poles parallel to the front mast. I ordered galvanized steel pipe, seems all the hardware will cost me around Usd 1000 here.

I think for sure there will be implications with the steering, so I guess I'll have to modify the rudder or build a better one later on. I planned to do that anyway, fishtail or articulating - as some of you here have demonstrated success with.

If this first install don't work out to my satisfaction, I *could* build a new mast on top of the wheelhouse. Similar to that some of you here have, with supports going down to the deck/bulkheads/frames.

The front of the wheelhouse is around 1/3 of lwl from the stern, my only concern is changing the boats appearance. I would prefer to keep it looking 'traditional'. It's originally from 1943, btw.



Thanks again, V.

 

[McGillicuddy]

Jim
With only one boom out, the turning moment (rotational force) would be calculated as the moment f x d where f = drag of one paravane and d = the horizontal distance from the centerline of the mast to the tip of the boom (not the length of the boom unless it is completely horizontal). It is the distance from the centerline that provides the multiplier in the calculation. The boat is not rotating about the forward connection point, it is rotating about the mast.

I can see why you think it does ‘pull’ the bow around. It seems logical that it would. The calculation of force on the rigging is separate issue and would be used to correctly size the rigging for the loads applied. You would also think the forward stay would reduce the torque on the mast by alleviating the backward pull of the paravanes and it does do that to the extent of the load is applied to the forward stay. But this does not apply to the theoretical calculation of where the load is considered to affect the vessel.

By the way, all the calculations applied to the boat that make up both horizontal and longitudinal stability are theoretical positions. But they seem to have been working out just fine for the last hundred years or so. Guys working in finite math have refined and model tested the heck out of the calcs and would laugh out loud at how crudely I have described the math. But in the end the finite calculations would be within 0.5% of mine. So I am okay with that. [emoji106]


Cold Smoked:
Nice boat. If it worked well as a trawler since the 1940’s, is there an issue now that makes you think you need a different type of rudder? Is it underperforming in any sort of meaningful way? If not, I don’t understand the urge to spend significant cash. If you think that the steering characteristics are going to change substantially by running paravanes from the forward mast, I would strongly suggest a sea trial first with the paravane installed forward to see how it handles. I suspect you will find the steering is still good. No need to change either mast position or rudder unless you are doing it for aesthetic reasons. One advantage of having the mast forward rather than over the wheelhouse is that the entire system is in view from the helm while I operation. I agree with trying to maintain the original character of the boat. I think that is a lovely idea..

 

[Cold-smoked]

Jim

Cold Smoked:
Nice boat. If it worked well as a trawler since the 1940’s, is there an issue now that makes you think you need a different type of rudder? Is it underperforming in any sort of meaningful way? If not, I don’t understand the urge to spend significant cash. If you think that the steering characteristics are going to change substantially by running paravanes from the forward mast, I would strongly suggest a sea trial first with the paravane installed forward to see how it handles. I suspect you will find the steering is still good. No need to change either mast position or rudder unless you are doing it for aesthetic reasons. One advantage of having the mast forward rather than over the wheelhouse is that the entire system is in view from the helm while I operation. I agree with trying to maintain the original character of the boat. I think that is a lovely idea..

Thanks, and yes - my plan now is to try it first with the front mast. The rudder performs less than satisfactory at slow speeds and when going astern. I am capable of modifying the rudder myself, so I don't think the cost will be high at all.


Thanks, V.

 

[McGillicuddy]

CS. You might want to look up Becker Rudder to help with your slow speed maneuvering issues. If you are handy with a welding stick you might be able to modify the rudder this way.

 

[Cold-smoked]

Yes, but I plan to make it as simple as possible.

This is my boats very crude rudder. I suspect the rudder is a bit too short, and the shaft is too close to the prop - so it doesn't get that much effect from the prop-wash as a more balanced rudder would. I did move that zinc, btw.

But it's too much work to change the position of the rudderstock/shaft, so I think I will modify it to something similiar to that of the second pic. Simple, cheap and easy to fabricate. I may add some steel angle bars on top and bottom to help direct the prop-wash.

 

[McGillicuddy]

Wow. Yes, I can see why you might want to modify that. That’s a really poor design. I guess that the original prop was a fixed blade type and located a bit further forward?

 

[Cold-smoked]

Yes, we agree. And judging by that sort of foil shaped/tapered piece of steel behind the prop, who ever made that rudder seems to have had a plan. I guess this was done in the 1980's.
And you are probably right about the prop originally being fixed blade and located a bit further forward.

 

[Cold-smoked]

The reason for installing paravanes, is that since the hold is pretty much empty/light now - the boat is quite stiff. It's 43 feet/60,000 lbs +, and has a heavy steel bilge as well as steel/concrete out on the sides of the bilge down in the hold area. It doesn't lean over that much, but it's snappy. With 6-9 feet of beam seas she leans over by around 10-15 degrees, but being inside the wheelhouse when that happens is not exactly comfortable.

Obviously this is not a luxury trawler as many of you here have, but we enjoy to bring family and friends out for fishing and relaxation. We have been 11 at the most on day trips, a few of them even managed to get a nap down at the front berth/galley.

Paravanes will hopefully make all of this even more enjoyable. The climate here is similar to that of BC or Alaska, and the pleasure-boating season here is usually from ~april until october.

I plan to install the A-frame mast and poles on top of the gunwales, exactly where the main deck meets the front deck.

Just showing some pics from last springs(may) haul out and paint process.

 

[Larry M]

Here’s a thread from six years ago about building your own paravanes. Good luck with your project.

http://www.trawlerforum.com/forums/s31/building-your-own-paravane-system-6339.html

 

[Cold-smoked]

Thanks a lot, Larry. I had a look at that, and I do have a plan now. I love your boat and set-up, btw.

 

[Xsbank]

I'm late to this thread but I think if you mount the paravane poles too far forward you will stress the rigging with the pitching motion combined with roll...

 

[Cold-smoked]

Yes, I agree - but I will give it a try. If you had a look at the first posts here, there seems to be people who have been ok with this. But I do think that 25% to 50 % of a boats lwl from its stern is the perfect polemount location.

This is why I'm doubling up on the A-frame mast that I already have.. I will be using a total of 4 pipe stays as well as a few steel wires.

 

[Xsbank]

I forgot (I don't know how) to complement you on your boat, its gorgeous! I am off to Google Tromso to see where you are. My paravanes are not used very often on our inland sea and I believe they were not used very much by the previous owner as the boat was delivered with the poles etc. lying on the deck. I have reinstalled them and I have a roll of 1/2" braid to replace the three-strand because the braid is easier on my hands, but my "fish" are too heavy for me without the blocks to lift them aboard. I will try and post a photo that shows them... I have also removed the "bow thruster" and its cut up for other mounts. My poles are amidships...

 

[Cold-smoked]

Thank you, Xsbank. You have a very cool looking boat yourself, it looks very sturdy too.

I plan to install blocks and/or sailboat winches for retrieval of the vanes, similar to what Larry M has. I'm sure those winches are very useful. I had a look on ebay, it seems I can have a pair of used ones for around Usd $100.

Did you notice any negative effects of your poles being amidships ? I would love to see more pics of your boat and paravane set-up.

 

[Xsbank]

Not so far. The boat has a very flat deadrise and a sharp chine so it rolls like a Grand Banks which is comfortable enough until its not! The fish are very heavy and it took some changes to the tackle to make it easy enough for me to lift them in and out but if the boat were lively and you were trying to retract or deploy, these giant heavy steel weights would be swinging about at chest height, not a good situation. But in the water they work fine. Its not possible to tell how much of a speed penalty there is because I have never tested that parameter.

Because you hoist the fish by hand, that is why I have bought but not yet spliced the 1/2" braid.

My procedure is to raise and drop the fish down beside the boat and then deploy the poles, reverse the procedure for retrieving. With your boat you will have to be careful of the hull's finish, with my aluminum boat, no worries.

I just bought a 2-speed sailboat winch to mount on the stern rail for retrieving a stern-tie line for anchoring. They can be had for good prices as long as the sailboater is not being silly. I looked for an hydraulic capstan so I could also use it for a pot-hauler for prawns etc but they are nowhere to be found at a reasonable price. Sailboat winches would be a good idea for retrieving the fish as long as they are mounted close enough to where you store the fish to have a hand to guide them to where they are stored, safely, if you want to be able to do it yourself.

 

[Xsbank]

Here is another: The white lines running forward at an angle to the cleats are the raising tackle. I stand at the base of the poles when I hoist to deploy the fish. The poles, being over vertical, need a good push to get them started to swing out, a bit of rolling helps! The poles are supported by wire rope, If these wires were not serviceable, replacing them with Blue Steel or Dyneema would be a good option as long as there was no way for the lines to chafe, the single worst enemy of Dyneema.

The two lines coming forward to a single point are the locating lines for the crane. She's not as scruffy now after a good wash...no, she's just as scruffy. New dinghy now and solar panels mounted aft, a new flag place, no winch cover... she changes rapidly!

 

[Cold-smoked]

Thanks for that, Xsbank !

Wouldn't it be safer to deploy the poles first, then the vanes ? That is what I had in mind and planned to do.

I also plan to make the vanes from ply and round off all the edges, and paint them with epoxy. I was also thinking of maybe having a simple guide rail for the retrieval cable, that flips out when needed. The guide could be running from in front of the sailwinch and then pivot a foot or so to the side of the gunwale. That way I think it could be possible to reel the vanes in almost all the way to the top, without touching the hullsides too much. Larrys Hobo has the winches installed higher up on the mast poles, so I think they do almost all of the lifting.

Your boat is looking good there ! Nice big flag and new dinghy, congrats !

We also want to get a new dinghy, but I worry that it will get stolen quickly. The city harbor where we dock is open and accessible to everyone. An inflatable would be very convenient for us, but for this old boat a wooden dinghy would be more appropriate I think.

Btw, can you catch any significant amounts of prawn there by using pots ? My brother and I talked about trying that here, but from what I've heard those who tried didn't get much if any. Trawling seems to be the only way here. We usually fish with bottom fishing reels, rods and long line. Fun, fun.