Paravanes boom position?

[Cold-smoked]

Very nice boat there, Simi ! What will the mast-system look like, and how does she roll - is she stiff or tender ?

 

[Cold-smoked]

Btw, I found this clip from a show that aired here 7 years ago. The experienced captain/host takes us around the coast in various historical boats. This piece is with a 75 footer, in 10-15 ft seas off the coast. The host is saying that the beam seas are terrible, and that he must try and stay on course. I can hear the swearing from inside the wheelhouse, possibly from the cameraman or the host himself And this is why I installed paravanes .


https://tv.nrk.no/serie/norskekysten/DVFJ67001309/sesong-1/episode-3#t=35m46s

 

[gsholz]

Regarding the position of the paravanes or flopper stoppers. I'm just re-reading Bob Beebe's book "Voyaging under power". He insists that the paravane rig should be positioned at 28% from the stern preferably at a bulkhead to deal with the stresses.

Putting it further toward the bow inhibits steering response as the paravanes fight any course correction. He also mentions increased drag the further forward the vanes are positioned. The paravanes will also try to prevent the bow from rising into oncoming seas the further forward they are. Beebe has a whole chapter on paravanes.

 

[Cold-smoked]

Regarding the position of the paravanes or flopper stoppers. I'm just re-reading Bob Beebe's book "Voyaging under power". He insists that the paravane rig should be positioned at 28% from the stern preferably at a bulkhead to deal with the stresses.

Putting it further toward the bow inhibits steering response as the paravanes fight any course correction. He also mentions increased drag the further forward the vanes are positioned. The paravanes will also try to prevent the bow from rising into oncoming seas the further forward they are. Beebe has a whole chapter on paravanes.

He is probably right in saying that 28% is the perfect position, but I feel fairly confident in saying that any position behind of CG/50% to 25 % of lwl is acceptable, if your boat has a good rudder. I found a strong area near 1/3 of lwl from the stern on my boat, and didn't even bother to check the % of lwl. It all works really well, despite my mediocre rudder.

 

[Simi 60]

Very nice boat there, Simi !

Thanks

What will the mast-system look like,

Because we have the height already the general consensus is a mast can be avoided and, it would seriously affect solar panel positioning and shading if we had one.

Should be able to get 45degree angle on the cable with what we have.

and how does she roll - is she stiff or tender ?

Carvel hull so she rolls.
Saying that, not as bad as many we have been on.
Happy enough to punch into weather without them but get any beam swell happening and all bets are off.

In the past we have been able to change course and essentially tack towards destination to stop it, but if we are going to put some miles on her as we intend, she'll need something better than that.

As she is our full time live aboard house we are a very much wait for the right weather window type of cruiser so reality is she shouldn't be seeing anything to bad.

 

[Nightsky]

For your consideration, close enough to 50% mark and position of arm if done in the front location

IMO, the forward location would offer a more effective location for the poles. The fish would drag back to just aft of amidship, which is acceptable. No need to worry about the fish flying out of the water if you have them deep enough and that the fish are angled/pointed downward. The amount of weight on front end of fish has some bearing here. I used to have my fish 4-5 fathoms below the surface. This may be too deep if you do a lot of shallow water anchoring, but then you could just shorten them up in those occasions only.

 

[McGillicuddy]

Here is a very similar wood boat with the booms at the aft end of the house.

 

[Simi 60]

I wonder why they put them so high?
If they ran them from the deck down the angles and loadings would be a lot better.

 

[Larry M]

Most Nordhavn’s mounted their paravanes from the boat deck. Loading must have been ok but I know you what you’re saying from looking at it.

 

[McGillicuddy]

I wonder why they put them so high?
If they ran them from the deck down the angles and loadings would be a lot better.

The boat was originally a ‘head’ boat so would have 25 people on each side with their fishing poles hanging out hoping to hook something. Putting the paravane hardware in the second deck kept it out of the way of the great unwashed.

 

[Cruising Sea Venture]

Sea Venture Refit is Done - New video posted

For those interested, we have now finished our refit, which included a new superstructure and paravane system.

We are now headed to SE Alaska and Glacier Bay for the summer. We will return to Puget Sound in the fall and then in 2019 head south to Mexico and beyond.

 

[MurrayM]

Thanks a bunch for posting that! It should be a game changer both for stability and heightened camera angles

If you don’t mind...how big were the backing plates in the pilothouse walls & roof relative to the outside mounting plates?

 

[Cruising Sea Venture]

Paravane Superstructure backing plates

The backing plates in the pilothouse are the same size as the exterior pads and are aluminum 3/8" plating.

For the stern feet of the superstructure they are much larger, since these feet take the majority of the load.

All the bolts are tapped through the fiberglass, which has a minimum thickness of 1/2 inch then backed with the aluminum plates and bolts.

The back plate bolts are 1" bolts on the exterior and 1/2" bolts on the interior side. The forward feet in the pilothouse are all 1/2" bolts.

The back feet are positioned directly over the salon wall where it intersects with a 2nd wall. 1/2 the bolts are on the outside of the house, and 1/2 the bolts go to the inside of the salon. The inside bolts are hidden.

Here is a picture of the rear feet exterior backing / chain plate.

I hope this helps. It's not a very good picture with the sun this morning, plus it came out sideways! I think it's shown in better detail in the video.

Jim

 

[Larry M]

Nice job! You did a great job on the tower. I hope you keep posting on your travels.

 

[MurrayM]

The backing plates in the pilothouse are the same size as the exterior pads and are aluminum 3/8" plating.

For the stern feet of the superstructure they are much larger, since these feet take the majority of the load.

All the bolts are tapped through the fiberglass, which has a minimum thickness of 1/2 inch then backed with the aluminum plates and bolts.

The back plate bolts are 1" bolts on the exterior and 1/2" bolts on the interior side. The forward feet in the pilothouse are all 1/2" bolts.

The back feet are positioned directly over the salon wall where it intersects with a 2nd wall. 1/2 the bolts are on the outside of the house, and 1/2 the bolts go to the inside of the salon. The inside bolts are hidden.

Here is a picture of the rear feet exterior backing / chain plate.

I hope this helps. It's not a very good picture with the sun this morning, plus it came out sideways! I think it's shown in better detail in the video.

Jim

Thanks

 

[gsholz]

Nice video. Really drives home the size and cost of the superstructure required for paravanes. Seems like the costs of paravanes, fins and gyros are not all that far apart in the end.

Be careful launching those fish in rough weather. Always good to deploy them before you need them.

 

[Cruising Sea Venture]

More videos to come

Nice job! You did a great job on the tower. I hope you keep posting on your travels.

We will keep posting the videos. They are a fun hobby, and we have got to meet and connect with so many boaters it's been a real joy.

Thanks,
Jim and Rosy

 

[Cruising Sea Venture]

Paravane launching

Nice video. Really drives home the size and cost of the superstructure required for paravanes. Seems like the costs of paravanes, fins and gyros are not all that far apart in the end.

Be careful launching those fish in rough weather. Always good to deploy them before you need them.

Yes, we will follow the rule, if your thinking about it, deploy the fish, and once deployed, they stay out until calm.

I agree on the cost of the different systems. It's been ask about so much I'm working on a video that goes through how we selected paravanes vs. fins vs. gyro for stabilization.

Thanks,
Jim

 

[Dashash]

I know this thread is a few years old, but thought I'd use the opportunity to solicit opinions from the experts.

I'm toying with paravanes myself. The boat is an '80 Bristol 42, full displacement, round chines, twin. About 15 tons. She rolls.

I currently have a mast, but it is surely undersized for much more than a steady sail. I sketched up a rough idea of the kind of configuration I think would suit my particular dimensions. It is based on an a-frame set-up I have seen a few times in this thread. My primary concerns:

1. If I can transfer the force from the fish downward on the a-frame vice the mast (or at least a good portion of it), I wonder if I could keep my existing mast? The mast has a decent mounting plate (5x7"), and the mast itself is 3x5" solid wood.

2. The fore and aft stays for the mast.. Need to figure out how much load these need to carry. With the brace bars on the booms, I think not much.

Obviously, everything depends on the actual forces involved. This is just me thinking out loud. A loads analysis is obviously required before I can move much further along in the design.

General thoughts?

edit: (red indicates stowed configuration, blue/green is deployed)

 

[slowgoesit]

Personally I think you will need to upgrade your mast. On our boat, the mast is stepped all the way down to the cabin sole, with a steel framework distributing loads to the keel. From the pic of your mast step, I don't believe it will be up to the strain of paravanes. Your paravane system is just that, it needs to be a SYSTEM, with all parts designed to handle and disburse the considerable loads transmitted to the mast, from the paravanes. Probably not what you wish to hear, but I think you need to get a Marine Architect involved.

 

[Dashash]

Thank you for the thoughts. I have to agree.

Though in my searches, I came upon this interesting set-up that doesn't seem to rely on the mast for support. I toyed with the idea and re-drew the sketch. Attached a picture of what I'm talking about.

 

[Cruising Sea Venture]

The only thing I'm an expert in is writing checks, but I can throw in my 2-cents worth. On Sea Venture, the naval architect never considered using our mast that was not designed specifically for paravanes. We have an A-Frame to distribute the load to 4 points, and the mounting plates and backing plates are all very robust. The loads can be tremendous. The bigger the system, the greater the loads, the greater roll reduction will be obtained. It's not some simple math, and I would have to agree with slowgoesit, a naval architect, who is experienced in paravane systems, is needed.

A couple of items I did notice from your diagram. I don't see any support from the end of the pole going forward. The force pulling the pole toward the stern is as much as the pull on the mast. Keep in mind, when cruising with paravanes, the fish themselves should be about even with your stern. The line running to the paravanes will most likely be sitting at around 45 degrees at cruising speed. Also, I didn't see a way for the pole to be locked in position when out. This is needed to keep the pole from bouncing inward when the fish are not deployed. Note once installed you will run with just the poles out, no fish. This reduces the rate of roll and makes for a more comfortable ride when the fish are not needed in the water. Lastly, the connection point of the pole can not be overlooked. The same force that is pulling on the superstructure will be trying to drive the end of the pole into the boat. A simple connection to a rub rail or cap rail will not be sufficient. While Sea Venture is quite a bit heaver (45 tons) and thus the system much bigger than you would require, I think its easy for people to assume it's less expensive than other types of stabilization.

I have no idea of the naval architect we used could assist you to some degree remotely, but if not, maybe he could help you with how to locate a qualified naval architect. His name is Johnathan Moore with Tim Nolan Marine Design in Port Townsend, WA.

The results we have had are fantastic. Think 10' to 12' beam seas. Pre-paravanes rolling 40 degrees each way. With paravanes, less than 10 degrees each way. But it did not come without a price. Our system was quite expensive, more than active fins would have been, but for us, a better choice.

Best of luck on your project.
Jim
M/V Sea Venture
www.CruisingSeaVenture.com

 

[Dashash]

Jim,

Thanks for the advice. I've reached out to a few NARC/marine engineering companies here in the Chesapeake/Annapolis area. If I hit some dead-ends I will reach out to your contact in WA.

Agree with you on all your points. Of course, my sketches are entirely incomplete. Regarding support from the poles going forward - I attempted to illustrate that design element by drawing the line from about 1/3 up each pole to a point on the hull forward a few feet from where the boom is mounted. In the actual design, this structural member would most definitely have to attach higher up on each pole and probably extend further towards the bow.

Thanks for sharing your results. That's an incredible improvement.

 

[Larry M]

The mast on Hobo doesn't have a compression post. The mast is for looks and lifting a 800 lb dinghy. The A-frame takes and distributes the load. The A-frame design is pretty common in the PNW where ours were installed.

I’ve posted this before to show the loading. In big seas you can here the rigging singing as it loads and unloads going through the water.

 

[Alaskaflyer]

There is a steel passagemaker for sale in Anacortes with a paravane system that is not connected to a mast. Rigging for extending/retracting and supporting the poles is instead attached directly (somehow) to the pilothouse roof.

 

[Alaskaflyer]

It has a mast with a boom and tackle, but the mast is not connected to the paravane system at all. Instead you can see the tackle between the upright pole and the house roof. The pic is a little confusing, they must use the boom tackle to assist in removing the fins and positioning them for deployment, as it is currently attached to the port fin in its storage rack on the stern.

 

[Dashash]

Interesting. The more I think about this from a statics perspective, I realize the moment generated from the fish can translate to a compression force on a mast (or a-frame) if one were used, but could also translate into a shear force perpendicular to the orientation of a mast. It really depends on what angle exists between the end of the pole and the attachment to the boat - whether that be to a boom or the top of the pilothouse like in the example above.

In terms of system performance, all that really matters is the moment that can be generated by the fish - a function of the horizontal component of the boom angle and the downward force exerted by the fish to counteract the boat's moment of inertia.

 

[Dashash]

The mast on Hobo doesn't have a compression post. The mast is for looks and lifting a 800 lb dinghy. The A-frame takes and distributes the load. The A-frame design is pretty common in the PNW where ours were installed.

I’ve posted this before to show the loading. In big seas you can here the rigging singing as it loads and unloads going through the water.

Do you keep your fore and aft guy lines on end of the boom attached/rigged all the time, or do you rig these only before deploying the fish?

 

[Lepke]

I was a commercial fisherman, I used flopper stoppers every day. My mast was wood, about 5" in diameter, mounted to a heavy beam at the deck level. Boat was wood, 55'x12'.
The trick is adequate shrouds and stays supporting the mast. Your mast may be ok. The booms when set go out at about 45°. Any lower and you risk them going under in a big wave and then your rigging earns it's money. I did it 3 times in about 30 seconds w/o loosing anything.
The further out from the boat sides, the greater the effect on stopping rolling. If you're going to run with the floppers out, the boom needs to be stay'ed fore and aft. If you use the commercial kind of floppers, there's a row of adjustment holes. They set the angle. Forward holes are good for running and aft holes tilt the nose down, making the flopper act like a brake. Good if you need to slow for trolling.
As I remember, my shrouds were 1/2" galvanized wire rope. Stays running to the boom were 3/8" gal. wire. Stays had pelican hooks so they could be moved out of the way when the pole was in. My poles were trolling poles so much heavier and longer than you need. The floppers I used were the biggest made at the time. In fairly heavy seas, I could walk normally on deck. At anchor or drifting, the boat hardly moved. Rigging to the flopper needs to be strong enough so you don't loose them. Best if the flopper has some rigging independent of the boom, so if the boom breaks, you don't loose everything. Couldn't find any pics.

 

[JDCAVE]

I have the identical setup as Larry has/had on Hobo with the A-frame setup. Several KK42’s have this setup, and a couple I know of, that do not. Those that don’t have this design have resulted in failures. The loads that are generated are substantial and it’s a really a good idea to engage a marine architect/engineer to ensure you are not putting loads in areas that will result in a catastrophic failure.

Have fun!

Jim