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Tuesday, March 29, 2011

System Design

This next installment of the back story will cover the system design.

There are a bunch of things that have to be sorted out when planning an installation. They include:

- Actuator location
- Fin size
- Hull reinforcement
- Hydraulic power (pump)
- Electrical power
- Transmission interlock
- Speed sensor/pickup
- Hydraulic cooling
- Location of control unit, valve blocks, diverter valves, control display, and hydraulic tank.

Actuator location: This was the starting point. For planing hulls, the fins should be within the center 20% of the water line. The location also needs to be accessible for installation and maintenance. On the 47' EU, there really is only one possible place which is all the way against the forward firewall in the engine room. The location is 1.5' forward of the LWL center, so it's a nearly perfect spot. It can't go further aft because the fuel tanks are outboard against the hull. So that locates the actuator for/aft, and is one stake in the ground. How far outboard the actuator goes depends on the fins, so we'll skip ahead to that

Fin Selection: Fin selection also impacts actuator location, so selecting the fin is required to finalize the actuator inboard/outboard location. The bigger the fin, the more effective the stabilizers are at lower speeds. The 47 EU can cruise at 20 kts, and has a top speed of 24 kts, but I want stabilization at a more efficient displacement speed of 6-9 kts. This drove the selection to a 6.0 sq ft fin rather than 4.5 sq ft. Both are fine at the higher speed, and in practice are expected to lower cruise speed by no more than 1/2 kt. 7.0 sq ft fins would have been an option, but the bigger the fin, the more the actuators need to be moved inboard, and the less effective they become. The key is to keep the fin inside the limits of the hull when they are centered. In other words, the fin can't protrude wider than the boat's beam at the water line so if you are against a warf, the hull is making contact, not the fins. And they can't drop lower than the draft of the boat. The 6' fins fit with bringing the actuators about 6" in from their most outboard possible location - not a bad tradeoff. The 7' fins were more problematic and forced the actuators much more inboard with possible interference with the engine stringers on the inside.

For reference, the past installations that I was able to track down on this model boat all used 4.5' fins. Part of the challenge was sorting out the impact of using larger fins, and whether there was a problem that I didn't know about. Luck has been with me, and it turns out Grand Banks is doing an TRAC installation now using larger fins, in fact their project includes stabilization at rest (STAR) which uses an even bigger fin than mine. It's the engineering for this new project that I'm shadowing which includes placing the actuators more inboard that jobs they have done in the past.

The other challenge with fin selection is making sure they clear the hull across their full swing. My boat has a chine at the outer edge of the hull, and the fins need to be trimmed to clear the chine. A side benefit of the more inboard actuator location is that less trimming of the fins is required. I'll lose about 1/4 sq ft off each. I'll be templating the fin, and TRAC will built it with the required notch.

So that nails down the fins, and finalizes the actuator location.

Hull Reinforcement: As I've mentioned previously, the reinforcement schedule is borrowed directly from Grand Banks on a nearly identical installation they are doing, and that one is based on several past installations that they have done. It involves relocating the stringer and building up the hull thickness between the new stringer, the ribs fore and aft, and up the side of the hull. This is the part I know I shouldn't do. I just stink at doing this type of work, and this is not the project to learn/practice on, so I'm hiring it out through my yard.

Hydraulic Power: The fins are run off hydraulics, and there are two ways to power it. A pump off one of the main engines, or an electric pump run off the genset. I'm not a run-the-genset-all-the-time kinda guy, so electric is out. Besides, the stabilizers only work when the boat is moving, and the main engines need to be running to make the boat move, so that's the obvious answer. Then the question is how to attach the pump. In my case the answer is easy. My ZF transmissions have provisions for a direct drive PTO. I've ordered the PTO kit from my local dealer, and the pump mounts to the PTO kit. One more stake in the ground.

Electric Power: The stabilizers run of 24V, so my package from TRAC includes a 12V to 24V power converter. I've got a spare 30A breaker and am ready to go.

Transmission Interlock: The stabilizers have a safety interlock that centers and physically locks the fins when either engine is placed in reverse. This requires picking up some signal when the gears are in reverse. My ZFs are electro-hydraulically controlled, and TRAC offers pressure switches as one interlock method, so that's what I opted for. I still haven't figured out what plug ot remove and replace with the pressure switches on the ZFs, but I'm confident I'll sort it out somehow. If anyone happens to know the ZF hydraulics, I'd welcome any help I can get. My backup plan is to tap into the electric control and use relays.

Sensor/Speed Pickup: The stabilizer control unit needs to know how fast the boat is going. If I could wave my magic wand, the control unit would take an N2K input and pickup the speed from the ships GPS, or if you want to be old-school, use NEMA 0183 to get the GPS speed. But my magic wand isn't working, so I have to install a rev pickup on one of the prop shafts. It's OK, I'll get over it.

Hydraulic Cooling: This one isn't 100% nailed down yet, but the current plan is to install an oil cooler in line with the engine raw water intake. TRAC wants the water temp to be 90 deg or less. My engine generates a 10 deg rise in the raw water, so in any kind of tropical water, outlet water temp will be too high, so I plan to use the intake water. TRAC is supplying a cooler with a 3" water aperture. Cummins (engine manufacturer) specifies a max intake restriction of 5 in Hg, and at sea trial they measures 1.2 in Hg. The specs on the cooler indicate it will add about 1 in Hg of additional restriction, leaving the total well below 5, so I think this will be fine. That said, I'm trying to get Cummins to give it the thumbs up, but haven't been able to corner them yet.

Location of Equipment: All the other "stuff" needs to have a home. I've gone through and put post-it's up where everything will go, and I'm pretty sure it will all work, but I want to have the equipment in hand to be sure. Once I have the locations finalized, I need to figure out all the cable lengths, and TRAC will make them all to length. Same with the hydraulic lines, except I'll have them made up locally.

So, I think that covers the system design.

Comments and discussion on this post:

lorenzo_b: Just put paravane stabilizers on my boat, all manual, built the swinging booms and fins myself with 2K worth of steel delivered from Miami. The winches were lots of fun to make. About two weeks of welding, 4 hrs a day. Total cost 3K.
That's one good reason to go with paravanes.

drpohl: I appreciate your preparation and plan but did you ask your previous surveyor for recommendations? Did you ask your insurance company regarding these major changes if they will require a re-survey and/or incline test/stability booklet by a NA? Whenever making major changes get it signed off from all the major players - before proceeding and after its done - sea trial and demonstrate to your and the surveyor's satisfaction.
Keep us advised on your progress and additional steps taken

askaer: Dear all Grand Banks folks out there!
What a wonderful and comprehensive sharing of observations and research on the stabilizer project at owner's own hand. I learned a lot. Currently I am having the very same work done on our 1year old GB 47 EU "ALMA" - hull #88 - read more about her at www.askaer.com. On recommendation by GB yard in Malaysia, I went for Trac 220 -6 with STAR using port engine as hydraulic pump PTO under way and electrical pump (generator on) during anchor, if needed. The procedure stated by you seems similar to mine and for the reasons of the many risks stated, and the fact that we keep the vessel in Singapore, we were grateful to GB that they offered to take the vessel back to the factory for the refit. It is currently at it's completion phase and next month we are going to try it all out. We are happy to report further at that time.
Super with this forum. All our best wishes and good luck.

Tanglewood: Glad the hear from you , Heine.

For others on the forum, it's Heine's installation at the Grand Banks factory that I am shadowing, so I'm very grateful that he's one step ahead of me and that Grand Banks has so generously shared their plans.

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