Roll Stabilization

I'm trying to decide what roll stabilization to use on Portager and I would appreciate inputs from the list.

Since the Admirable isn't too keen on rough riding boats, good roll stabilization is a definite requirement. Since I need roll stabilization underway and at rest and I can't afford active roll stabilization that leaves steadying sails and paravanes. Since Portager will have a get home sail, I could use the sail for roll stabilization and avoid the added complexity of the paravane outriggers and launching and recovering them while underway.

So the main question is, which would be the most effective roll stabilization option. The sail or the paravanes?

Thanks in advance for your comments.

Cheers;
Mike Schooley

 

I have very little experience with roll stabilization beyong the use of a relatively small steadying sail that is aboard my fathers 36ft Cheoy Lee 'trawler'. The sail did have a noticable effect but the boat doesn't roll too badly anyway so we only used it a few times for the fun of it.
I would have thought that paravanes would be a much more effective stabilization system, but there are definite downsides to their use - such as a reduction in fuel economy and the danger that can be involved when they come out of the water.
The main reason for my post however is to suggest that you check out a couple of the recent issues of passagemaker magazine ( http://www.trawlertravel.com/cgi-bin/site.cgi? ) They had some very good articles on the design, installation and use of paravanes. (Can't remember exactly which issues sorry...)

 

'was just looking at their site myself and noticed that the current (May / June) issue has an article dedicated to this very subject

 

Built for but not with

Thanks for the response.

I think the need for roll stabilization is more dependent on the sea conditions and the distance between ports than the craft. I have heard from people that have cruised extensively that paravanes were mandatory on the West coast of the US but rarely used on the East coast.

You are right about the risks/danger involved in launching and recovering paravanes and the impact on fuel consumption. In addition, on a semi-displacement hull, I'd need to slow down to displacement speed in order to use them.

I have done enough research to be 99% convinced that I don't need paravanes and I'd rather not have the additional equipment to erect and stow every time I launch and recover the boat.

My main concern is that I have heard that it can be very expensive to retrofit paravane outriggers onto an existing hull that wasn't designed for them. I think I'll have Portager designed and built to accommodate paravanes but leave them off until I decide I need them.

Cheers;
Mike Schooley

 

Sounds sensible.
Once again I suggest a look at one of the passagemaker articles. (and once again I don't know which one!) It details how an owner designed, built and fitted a set of paravanes to his trawler. Well worth a read.
Have you considered fitting non active stabilisers to the hull? It would add to the wetted surface, increasing drag, but I would have thought that it would be more effective than the steadying sail. Depending on design, it would also allow for beaching of the boat - on the other hand, it may also complicate trailering....

 

Passive Stabilizers

Yes;

I am considering bilge keels. These will provide passive roll stabilization and improve the performance of the sail to windward. The bilge keels are more effective than small steadying sails but less effective that a large sail. In addition the inertia of the mast and rigging also help.

In addition they allow the hull to stand straight on a flatbed trailer, which could solve a parking problem and make it easier to ferry the truck and trailer.
Cheers;
Mike Schooley

 

Dear Portager

I spent 5 years in Brown Brothers working on fin, tank and rudder roll stabilisation. If you send me the outline parameters of your vessel (length, beam, hull midship, GM, Displacement, max speed, cruising speed) I can run some simplified simulations to show you the comparative advantages of fin, tank or rudder roll stabilisation potential. We have helped Wesmar inthe past, and they have a very competitively priced system for small vessels of your size.

Best regards

David Gray

 

David;

Thanks for the offer.

In the intervening 20 months since the previous post on this thread, a few things have change. One, I am now leaning towards active fin stabilization, but I’ll also have paravanes onboard for stabilization at anchor. I decided against paravanes because there have been a few mishaps retrieving them while underway. I’m leaning towards active fin stabilization because they are claimed to be the most effective option and the Admirable has a bad back.

The Admirable and I have decided to make Portager large enough that we have the option of living aboard after retirement. Therefore, our plans are now to make Portager 64’ long with a 12’ beam. The Metacentric height (GM) should be less than 5’ from the keel. Displacement will be 32,000 lbs light and 42,000 fully loaded. Speed will be 12 knots @ full load and 13.5 knots light. Long range cruising speed will be 8 knots.

Regards;
Mike Schooley

 

Bloody Heck Mike!...64'..! Can I come watch you back her down the ramp!

Have you looked at gyroscopic stabilisers? (Think that's what they're called. Mitsubishi makes them...I think...)

 

Suggested Fin Sizes

Dear Mike

I have run an enquiry routine, and attach the results. We note the Block Coefficient appears very low so perhaps you could check our input data and make sure we have everything correct.

You will note that we have shown perofrmance results for two sets of fins. They both give good performance in regular seas (about 90% stabilisation - shich is the market standard). You will not however that in irregular seas, this reduces to around 60% which is quite normal. In other words if you actually measured RMS roll before and after switching on the stabilisers, you would measure about 60% reduction rather than 90% in sea state 5. The larger fins do have a slight performance advantage in these larger seas as the fins are able to provide more lift before becoming saturated.

The gyroscopic stabilisers are produced by Mitsubishi, and were fitted last year to a luxury yacht in Italy. I think 3 were fitted down the length of the vessel. My impression of them is they are heavy, use a lot of power, and take up quite a bit of space. They have been around for a long time, but have never really caught on.

best regards

David Gray

 

The latest issur of Professional Boat Builder has a great article in the various forms of stabilazation.

A Combo would probably be best , long bilge keels to resist rolling at anchor & underway , a slosh (Framm) tank doesn't take too much room , and a mast for beam winds would be first choice.And perhaps get home power.

The paravanes could be simplified so launch & recovery was very easy , rather than a task.

The active fins are just another electric item with limited life hyd goodies and a HUGE price tag.

While it may sometimes work OK , parts in Patagonia may be a hassle , as may the first time you run aground or hit a Sea Land box at sea.

For cruising systems should be in depth , so the loss of any one does not ruin the voyage.The Bilge keels and slosh box have NO maint requirements.

FAST FRED

 

Hi

We have a tank model in our time domain simulator. I have added in a tank 1m long & full width of the vessel. results attached.

The tank as sized only reduces roll by around 10%. Tanks can be effective, and are not reliant upon boat speed. However, there are disadvantages to roll tanks such as audible sloshing noise, reduced static stability, increased rolling in long seas (low frequency), internal space requirements (best position is high up midships), increased displacement (typically around 4%) resulting in increased fuel consumption.

We haven't received our copy of PBB yet, but our general advice is there is no such thing as a free lunch in stabiliser selection - whatever method you choose has an impact which has to be weighed against the benefits and your operational requirements.

Have you considered Rudder Roll Stabilisation?

Regards

David Gray

 

Will;

How about if I post a streaming video to my web site? Just don’t expect to see what’s on the cutting room floor. I know that 64’ is a lot to transport, but if I make Portager nice enough, then I can convince the Admirable to live aboard and we can sell the house and retire earlier. We are still studying trade-offs, but our current range is 54' to 64'. At this size I expect to use lift launches more and boat ramps less. I’ll also park Portager at my local boat ramp, which the turning radius and ramp length (at high tide) to launch up to 75’. I will have to pay for two parking spaces though . I agree with David, gyro stabilization is brute force and it takes up too much room and adds too much weight. The need to make Portager transportable means we need to utilize the interior space efficiently and minimize weight.

David;

I think the block coefficient is screwed up because, 1 I gave you the LOA instead of the LWL which should be ~62’, 2 I gave you the overall beam instead of the beam at the waterline which is ~10’ and 3 the full load weight of 42,000 lbs is really for a 54’ length the weight for 64’ scales be 50,000 lbs, but since 50,000 lbs will require a larger tow vehicle I am hoping that we can find a way to keep the weight down to 42,000, 4 Portager is a light weight boat for her water plane area so the block coefficient should be a little low. Also the GM is a worst case number. I expect to get it lower since the air draft is <9’.

I started reading the Wesmar installation manual to get more info, but I ran out of time. I don’t plan to have 3 phase power onboard, actually I don’t plan to have an AC generator onboard, but I will have a hydraulic pump on a PTO shaft. Do you know if I can power the fin actuations directly? Also, I could not find info on Wesmar’s folding stabilizer fins. I think they will make transport highway easier since they would normally be sticking out like blades on a chariot.

FastFred;

It is good to hear from you again, but I have to agree with David. All roll stabilization options involve tradeoffs and active stabilization appears to be the most effective option. If I decide to go with twin props to reduce draft, then I would probably use bilge keels, but that would be primarily to protect the props and I’d still opt for active stabilization. OTOH, reducing draft produces directional control issues in heavy seas so that’s another tradeoff. I had considered sails for roll stabilization and a get home sail, but the rigging is a pain to erect and stow for launch and recovery and I’m already pushing the height limit for transportability. Stowing the mast would be very difficult so I opted for an auxiliary engine instead of the sail. The advantage of active roll stabilizers is they do not add height and they are very effective. The Admirable has a bad back so the more stability means fewer restrictions on Portager’s allowable sea state in the Admirable-onboard operational mode.

Regards;
Mike Schooley

 

"I had considered sails for roll stabilization and a get home sail, but the rigging is a pain to erect and stow for launch and recovery and I’m already pushing the height limit for transportability. Stowing the mast would be very difficult "

With a Motor sailor the rig is very low and a full battened sail would help with the area .

Simplest I have seen to handle a mast off the shelf is a flag pole raising unit from the local Skool.

These can lift a 30 40 ft mast with ease by turning a crank.
There is a 1/4 of circular toothed gear about 3 ft in diameter, and a small toothed wheel atached to the crank.
Unfortunatly the ones I have seen were galv , and too heavy for you , but aluminum might be avilable.

The other EZ solution is a Lutchet. In this case the mast is pivoted as in a tabernakle , but the heel of the mast pivots to the keel and has some counterweight.

The "trick" is a hatch that opens alowing the mast to pass thru the deck std. on old Thames barges for sailing under bridges!

AS a set of floper stoppers works well and requires a "mast" for a good angle for retreval ,
and a get home sail requires a mast , a combination into one unit would make sense.
Roller jibs can easily be made to store easily, simply have them built with light chain to roll arround instead of hard to coil wire.

Are you planning to live in the boat while on a trailer? as an RV?



FAST FRED

 

“With a Motor sailor the rig is very low and a full battened sail would help with the area.”

This is a perfect application for “Junk” sails which are low and fully battened. They use an unstayed mast which eliminates the extra rigging and the sails are much cheaper than conventional sails. I went a long way down that road before I decided I just don’t want to have to tend sails anymore. In addition stowing the mast and sail(s) below the 13’ 6” legal height limit on the trailer was going to be a big problem. Keep in mind the keel will be about 1’ 6” off the ground.

”AS a set of floper stoppers works well and requires a "mast" for a good angle for retreval ,
and a get home sail requires a mast , a combination into one unit would make sense.
Roller jibs can easily be made to store easily, simply have them built with light chain to roll arround instead of hard to coil wire.”

My setup will be similar to the Dashew’s design which is described at http://www.setsail.com/dashew/Deck_Tour.html . I’ll have a stub mast on centerline and outriggers on the outside corners of the deckhouse. The stub mast will extend down to the keel and it will be nested so that the extension sections stow inside the fixed outer cylinder. The center mast ******** mechanism will probably be pneumatic (compressed air) with locks at the end of travel. In the stowed position the top of the mast will be below the roof line so that the radar and running lights will be at or below the roof for transit. The height of the mast will be sufficient to provide a lever-arm to erect the outriggers which will stow either for or aft, depending on layout. The mounting point for the outriggers will be below the roofline so that in the stowed position they will be below the roof.

”Are you planning to live in the boat while on a trailer? as an RV?”

Yes, it has always been our plan to be able to stay aboard while on the trailer. Originally, this was to provide accommodations while in transit. We figured finding a place to park for the night would be easier that finding a hotel with room to park the boat and parking the boat and disconnecting the truck to drive to a motel would be a hassle. Now, the plan is to provide the ability to stay aboard for extended periods. This puts additional requirements on the boat/trailer combination, but that may be a separate thread.

Regards;
Mike Schooley