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SANAUH 03-13-2022 01:41 AM

Stabilizers - Gyro vs Electric Fin
While I realize this topic has been covered many times over, the question of gyro vs fins has new twist (pun intended) with the CMC’s introduction of an electric motor driven fin stabilizer for boats as small as 40’ (12m) (

I am having an SD trawler built (NPY45) and stabilization is a must have. We will be living aboard full time and will limit our travels to coastal cruising (Great Loop and PNW/IP) with time also spent in the Bahamas. Want stabilization while cruising (almost always at displacement speeds) and while on the hook (when unable to find a protected anchorage). Current plan is to have a large LiFePO4 battery bank, very large second alternator (Balmar 98 Series 24V/220a), and 2x 5KVA inverters with the goal of not having to run the generator when operating the stabilizer system or the stateroom A/C (Mabru 12MBTU 12V/44a).

As I see it, advantages to the gyro is greater roll reduction (mfg claims 76-95%, all reported numbers while at zero speed) and no protrusions. Disadvantages include long spool up time (28min to stabilization, 42min to full speed), periodic maintenance, and constant power demand (1.0-2.3kW). Advantages to the fins are instant on, no maintenance, less space needed in engine room, and lower total power consumption (0-1kW/0.1avg underway, 0-2kW/0.25avg at anchor). CMC claims 66-81% roll reduction (lower underway / higher while at anchor). Disadvantages are hull protrusions and less roll reduction.

So, for those that have experience with the latest generation of fin stabilizers… how effective are they really at reducing roll at displacement speeds (8kN) and while at anchor? Should I be worried about things getting caught on the fins (lines, kelp, debris) or them being damaged while cruising in shallow waters (e.g. Great Loop) or in the PNW where you might bump into a log?

The gyro we are considering is the SeaKeeper 6.
The fins we are considering are the Waveless STAB 20

mvweebles 03-13-2022 05:17 AM

I've run my boat with fins for 25-years. I just replaced the old vosper system with Wesmar.

First, they do take some engine room space. The hydraulic tank and the hoses do take up some room. Nothing like gyro, but not zero either.

Second, they do require maintenance. Every few years the fins should be pulled and the seals replaced. About $1500 or so added to the haul.

Third, while I have occasionally caught kelp, I have now installed a deflector in front of the fin that should make this tiny issue a none issue.

Third, I have zero concerns about the protrusion. Yes, in theory there is exposure. But in reality the risk is infinitesimal. But if you're the type to buy meteorite insurance, then it might be enough of a concern.

Fourth, even in open ocean conditions, I probably run my fins around 50% of the time though I am a bit of a sissy about choosing wx. And that's on the Pacific. In your intended grounds, would be much less. Fins are ideal - I have been known to turn them on for a ferry wake, then back off. But my boat is heavily ballasted with a very low profile so has a lot of inherent stability. Many boats require fins to be run constantly when underway.

At-anchor. My cruising grounds - pacific coast - is notorious for open roadsted anchorages. Some form of anchor stabilization is highly desired. I prefer flopper stoppers with outrigger poles. I store mine horizontally along the cabin side. They take about 10-mins to deploy and retrieve. They work extremely well and of course take zero power. Best I can tell, your intended cruising grounds would rarely need at-anchor stabilization so you may want to consider flopper stoppers rather than burden your underway stabilization system selection with a rarely deployed use case.

As an aside, sounds like you're trying to displace need for a generator and run off an oversized alternator and LiFePO4 bank. If so, you may want to rethink excluding the generator. The Loop and Bahamas will have heavy use of A/C not just for cooling but to retreat from bugs. But if you're including a generator too, then disregard. Also depends on how well ventilated the boat is. Although increasingly rare, some boats have decent flow-through and are very comfortable without A/C at-anchor as a result.

In closing, I agree that stabilization is a must. Seakeepers seem fine. Both systems (fin or gyro)! are expensive. The reason I will never own a SK is due to power requirements. It's just not how I like to run a boat. Nothing wrong with full-time generator use, just not what I want. I realize you're considering running off main engine alternator which mitigates much of my concern.

Good luck with your build.


SANAUH 03-13-2022 06:15 AM

Thanks for the quick and directed response. The Waveless fins are actually all electric (high torque electric motor mounted directly on top of fin). So no hydraulics whatsoever and therefore little space need in ER and little to no maintenance. And yes, still plan to have a generator, just want to avoid having to run it 24/7.

Waveless makes claims at being even more efficient with roll reduction while on the hook. One neat aspect of electric fins is that their ability to flip and operate in the opposite direction which eliminates “anchor walk”.

As much of fins performance is dependent upon the fin design and the system programming/response, hoping someone on this forum has direct experience with Waveless STAB fins and can speak to their effectiveness at anchor and at displacement speeds.

twistedtree 03-13-2022 06:33 AM

If sized accordingly, fins are very effective at displacement speed. I have no experience with the Waveless devices, but expect they would perform similarly to other fins.

The issue is that the slower the boat is moving, the more fin action is required since the fin is moving slowly through the water. The solution is to make the fins larger, and that solves the problem on a displacement boat. However, on a semi displacement boat the large fin creates disproportionately more drag at higher speeds and slows the boat down more. So it becomes a tradeoff between slower speed stabilization effectiveness and loss of speed and fuel efficiency at planing speeds.

When I installed fins on my previous Grand Banks 47 EU, I went through all this with ABT and ended up selecting fins that were one size larger than the typical install for that boat, all because I wanted good displacement speed stabilization. It was the right tradeoff for us since that's how we operated most of the time.

mvweebles 03-13-2022 06:41 AM

I obviously was not familiar with the Waveless brand. Can you post updates on objective reviews of both effectiveness and reliability? These may have been a better choice for my small boat than traditional hydraulic fins.

I do question ability of any fin system to provide meaningful at-anchor stabilization. Wesmar makes a partial claim that I have not tested. I suspect flopper stoppers are the way to go with fins, but that's just speculation.

Thanks for the research.


EDIT - since this is a new build, an option may be to go with seakeeper but but have hull blocking for fins installed so they are easier to install later if desired.

From observation, I'll echo Twisted Trees comments about upsizing the system. Of the negative comments I've read about stabilizer effectiveness, I'd guess almost all are related to system being too small or trying to reduce the $$$$

sunchaser 03-13-2022 07:29 AM

Listen to TT and Weebles carefully. They are both with hands on experience on this subject. I question the use of electric or air powered fins Vs hydraulic for three reasons.

First, a propulsion engine PTO and hydraulic system if designed into a new build will not take up much space. The power draw is easily handled by hydraulic motive power when underway.

Secondly, electric or air operated fins will not have as quick a response time as a hydraulic systems thus lowering their effectiveness. I spent over 50 years in industrial applications using all three. By far the quickest movement is via hydraulics. As example - trucks, loaders, backhoes and airplane actuators that require rapid and high power movement are mainly hydraulic.

Thirdly, bigger alternators, battery banks and inverter chargers are with their own space requirements and costly. Sizing and designing these for normal house use is a well understood and simple exercise. Once into powering stabilizers electrically you are into largely uncharted territory.

There are thousands of satisfied hydraulic system stabilizer users out there. When properly designed and installed they work marvelously and are trouble free.

A few years ago we were quite interested in a Grand Alaskan. It had air actuated active stabilizers which required a large compressor and genset operating to power the 7.5 hp motor. Upon closer inspection I had my doubts about the overall setup and walked. Last year I met the new owner and asked about the setup, he said he doesn't use it.

So my choice is go with an ABT, Naiad or Wesmar hydraulic setup that has stood the test of time. Then your onboard house electrical systems can be smaller, cheaper and working under well established conditions.

SANAUH 03-13-2022 07:46 AM

All good info. High torque electric motors have advanced considerably in recent years (e.g. Tesla). The STAB20 Waveless units are spec’d at 80deg/sec rotational speed. Not sure how that compares to oil based hydraulic units. Agree on air driven units. Also CMC has been producing electric direct drive stabilizers for 10 years to the large yacht market. The waveless units are a recent addition to enter the smaller boat market. The research I’ve done gives some confidence they know what they are doing. Again, hoping to hear back from someone with first hand experience.

sunchaser 03-13-2022 08:09 AM

Electric stabilizers for large yachts can be a valid application for two reasons. One, if no site specific hydraulic pump is employed, the hydraulic line runs from the ER are quite long. Secondly, large yachts are 24/7 with large Gensets thus opening the door for a variety of stabilization designs.

On our vessel the hydraulic line runs are very short and systems totally accessible. The same should apply to an NP 45.

rslifkin 03-13-2022 08:12 AM


Originally Posted by sunchaser (Post 1084867)
Electric stabilizers for large yachts can be a valid application for two reasons. One, if no site specific hydraulic pump is employed, the hydraulic line runs from the ER are quite long. Secondly, large yachts are 24/7 with large Gensets thus opening the door for a variety of stabilization designs.

On our vessel the hydraulic line runs are very short and systems totally accessible. The same should apply to an NP 45.

I'd think electric makes sense at the largest end as you mentioned, but also at the small end where you don't need hydraulics for anything else and the system is small enough that the power draw isn't all that huge. It's in the middle where hydraulic is almost the only viable choice.

Hippocampus 03-13-2022 08:22 AM

Will speak for the other side. Have Seakeepers. If coastal and in bays or rivers there’s no need for either. With SK you have nothing outside so no parasitic drag. I’ve just owned my current boat a short time but as they say “it not if you’ll run aground but when”. Going into to a new to us harbor on a moonless night (Deltaville) did the dirty and went into the mud. Could just back off with no issue. I remember the winged keels on sailboats. They were anchors if you went into the mud. So beyond the remote risk of penetration of the canoe body think the real downside is fins can complicate things in skinny water.
Other issue is junk in the water. Going through the C&D there was significant junk. Most just under the surface so not seen. Apparently flood pools were opened so tangles of branches with their leaves still on them would brush on the hull. I wouldn’t be concerned about injury to the fins in such a situation as they are strong. But would be concerned about potentially dragging that junk along. On that occasion looking over the side could see mats of this junk many feet across.
Lastly was impressed once you get up to ~10kts. or better my SD has a very stable ride even in a beam or nearly beam sea. You still get heave and some pitchpolling but surprisingly little roll. Talking to other owners apparently this is common behavior. Yes wind up is slow but you can alter course a little (even tack a bit) and increase boat speed until the thing is at operating rpms.
Agree running it at night seems wasteful. Personally thinking of putting a flopper stopper (not fish) on one side. SD hulls having more form stability tend to roll less at anchor. Probably don’t even need a pole as we’ve left the Caribbean so no dreaded north swell.
P.S.- think if you go with a gyro get one in a vacuum. Less resistance, easier to get to a high rpm so less energy to get there and stay there.

Finally, given this is a new build wonder if you looked at Magnus effect devices. Think you have exactly the set up where they would shine. Retract in skinny water or not needed. Deploy as needed. Effective at slower speeds or when still.

rslifkin 03-13-2022 08:35 AM


Originally Posted by Hippocampus (Post 1084873)
Lastly was impressed once you get up to ~10kts. or better my SD has a very stable ride even in a beam or nearly beam sea. You still get heave and some pitchpolling but surprisingly little roll. Talking to other owners apparently this is common behavior. Yes wind up is slow but you can alter course a little (even tack a bit) and increase boat speed until the thing is at operating rpms.

That's a big thing for SD and planing hulls. Once you get up to a speed where there's significant lift acting on the hull, roll gets damped a lot. The boat will still pitch unless you're really moving fast, but many hulls will start to pound before that point.

Going slow, the boat rolls, but the lift acting on the hull at higher speeds turns that roll into more of a series of gentle, well damped tilting motions. So instead of the boat rolling, overshooting a bit, rolling back, etc. it's just "tilt one way, pause, tilt back the other way". Basically there's no momentum to the roll.

To me, the 2 big downsides of the Seakeeper (and the competing gyros from Quick) are the significant power requirements for all but the smallest units and their rather large size (plus the weight). The appropriately sized Seakeeper for my boat (model 5) is almost 900 lbs and it draws between 1 and 2.3 KW. It's also approximately 30x30x25 inches. Between the size and the weight, I can't think of a single place on my boat it could be mounted on my boat, save for right between the engines (and you'd lose most of your access to the inboard sides of the engines).

Hippocampus 03-13-2022 04:24 PM

Different folks-different boats. On NT42/44 the space in the middle under the aft cockpit is ideal. There’s a hatch right there stock and the stringers are already brought all the way aft. There’s adequate space to get to all four sides of it. So no modifications required. You do lose the space for what would be otherwise storage and do put significant weight back there. But putting your heavy liquids (coolants oil etc) under the forward stairs or under the master queen berth balances things out. As part of our refit raised the bootstrap and bottom paint a fraction over an inch to compensate.
Unfortunately there’s no free lunch with anything. It’s so easy to just let thing be spooled up all the time that before Ukraine would have just left it on. Now will do that only when needed. Don’t think it will jump the fuel bill up much used like that.

Curious. What’s the draw and economics of Magnus.

Insequent 03-13-2022 04:30 PM

For fins the maintenance is seals every 3 years (Naiad) so it is not a big cost. I just leave them on all the time so that wakes are a non-issue. I've become very used to the boat sitting flat, almost zero roll, when cruising.

For SK, I'm yet to see any reliable numbers for maintenance intervals and cost. But there are a few rumbling noises around the yards about "those little details" and in a number of boats the SK's are coming out as the owners are unhappy with that. If anyone has been having serious conversations with SK I'd be interested in what they say about the maintenance aspect when pushed (and push hard is probably what you will have to do to get an answer).

Hippocampus 03-13-2022 04:54 PM

We just did entire maintenance using SK certified tech. Figured it was put in 2015 so wanted it ripped apart and have a serious look see. Same money as seals, bearings and flushing hydraulics etc on equivalent sized fins. Don’t have enough experience to give long term costs.

Hippocampus 03-13-2022 04:57 PM

Specs for our 5

Insequent 03-13-2022 05:16 PM

Hippo thanks for that.

Here's some info on a 60' plus boat a friend was looking at. Part of the reason he walked was the SK unit. It had an M21000 installed, which is now obsolete and most parts no longer available. (Sounds like Volvo of old, doesn't it?).

Apparently they are rated for 10,000 hours, but with 7,000 hours on the unit already the expert advice was 50/50 chance of getting the remaining 3000 hours. Turnkey replacement unit (including 20% discount) was over AUD$180 k.

Now one hopes that the current designs have eliminated many of the M series issues. And yes, it was a larger unit than 45-55' boats will use. But questions still remain IMO.

BandB 03-13-2022 06:50 PM

First, I would not select CMC's waveless. Too many proven systems I'm familiar with and have used to go that route. If going for fins, I'd go for Zero Speed and use Naiad, ABT, Wesmar, Humphree, or Sidepower. My personal preference is Sidepower Vector Fins on a boat that size. They are not sold as zero speed, but do very well at anchor. Sounds like you got quite a pitch from the Waveless salesperson and I'd believe only a little bit of it. I do prefer hydraulic fins but electric can be fine.

Second, however, on a boat that size and speed many would choose Seakeeper and not worry about having to use the generator. Anchor and slow speed are where they really excel.

Your biggest challenge is finding a professional installer and getting a full system design as you will need strengthening and a good solid base to take the added weight and pressure. Design and location limitations may make your choice of system for you.

mvweebles 03-13-2022 10:42 PM

My Vosper hydraulic stabilizers were 50-years old when I replaced them. Many Hatts also replaced but not until a good 35-40-year mark. They were still working but some important parts were obsolete so I retired them. There is now some fancier electronics and controls, but the new Wesmar I installed are more or less the same core technology. I've run my boat through mud and sand and never had an issue with my fins. But some people worry about stuff like that so fins may not be a good choice for them.

Because of my small boat, choices were limited. In my opinion, #1 is ABT, Naiad behind them. I experienced severe customer service issues with Wesmar and therefore I personally cannot recommend them, but their product is sound and they have history.

OP - you really need to think about what problem you're trying to solve. Given 50-years of successful service, half of which under my ownership, I have a hard time recommending something else. Hydraulic fins just work. And keep working. Not sure this is the place for new-kid-on-block.

EDIT: this bears repeating. Hydraulic stabilizer technology has been stabilizing boats for almost 60-years. Of all sizes. Of all types. Tens of thousands of installs. You have to search long and hard to find failures beyond worry-wart "what if the fin breaks" concerns. There are now very sophisticated controls that are added. What exactly is the problem?


SANAUH 03-13-2022 10:55 PM

At this point the biggest hesitation on SK is the required maintenance and expected life. We will be cruising FT without a home port. Do not want to be burdened with finding a SK factory tech every 3 months just to maintain the warranty. I can and will do most boat PM myself, but SK states that all maintenance/service must be done by a factory rep. Also have concerns about the expected life of a $60K piece of gear. I understand everything needs to be maintained, and many will need to be replaced, but the timing and cost of both have to get factored into the decision matrix.

SANAUH 03-13-2022 10:59 PM

The only reason to look at electric stabilizers is for stabilization at anchor. I know many mega yachts will install both fins and gyro to address this issue, but clearly not something anyone should/would consider for a 45’ boat. I do appreciate your point about sticking with proven technology and that fins just work. Hoping someone can share personal experience with CMC electric fins if not specifically their Waveless version.

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