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  Modifying a Hullavator
  Posted by: old_user on Jan-05-13 1:59 PM (EST)
   Category: Other Gear 

Got a couple of high vehicles so bought a used Hullavator yesterday. Gas springs are worn so I plan to replace them. Has anyone replaced the gas springs with higher rated ones? Lift is rated at 40lbs so I assume each spring is 20 lbs. I was thinking of swapping in some 30lb or maybe even 35lb springs to increase the lifting power since I have heavy boats. Anyone tried this? What was your success?

Kerry

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Messages in this Topic

 

  How old?
  Posted by: Marshall on Jan-05-13 3:52 PM (EST)
How old is are the units? Be careful if it they are early models. The locking pawl wasn't great on those so the extra oomph of your planned upgrade could give you an uppercut when you don't expect it.

Interesting upgrade idea though. Post how it works out.

See you on the water,
Marshall Seddon
The River Connection, Inc.
Hyde Park, NY
www.the-river-connection.com
hudsonriverpaddler.org
 
 
  age
  Posted by: old_user on Jan-05-13 4:11 PM (EST)
It's an early model and I've read about the locking problems. Looking at the mechanism it seems possible that the locking 'pawls' could be bent a bit to improve the latching. McMaster Carr sells the gas springs of varying poundage in the correct length and the correct end fittings can be screwed on to them I think. I also suspect that a heavier spring would solve part of the problem that people complain about--the two hullavators not rising in parallel. One issue with replacing the gas spring is that the outer end is held in with a long rivet and there's not much room between the ends of the rivet and the outer housing which drops down over it for a standard bolt. The rivet on the inner end can easily be replaced with a bolt.
 
 
  Lifting Capacity Definitions
  Posted by: guideboatguy on Jan-05-13 8:12 PM (EST)
-- Last Updated: Jan-05-13 8:48 PM EST --

Check the rating on the existing cylinders - it's often printed right on them, or you can measure it with a bathroom scale. If Thule says the device is rated to lift 40 pounds, you can be sure that the force applied by the cylinders is greater than that, most likely MUCH greater. That's because, due to their placement relative to pivot points and load location, the cylinders are working at a mechanical "disadvantage".

You can see this same principle on the lifting cylinders for the back window of a pickup topper. On my current work pickup, a pair of 20-pound cylinders won't even hold the window up. A pair of 40-pounders is overkill, but it's what I could get my hands on. The whole window probably only weighs 18 pounds, so just ONE 20-pound cylinder could hold the window open if the force were not exerted in such a disadvantageous manner (the force that must be applied fairly close to the hinge point is huge in comparison to the weight of the window that is actually lifted).

The same principle applies to your Thule Hullivator, but the difference between lift capacity and lifting force that must be applied by the cylinders will depend on the geometry of the device. **Edit** Okay, I just looked at pictures of the thing online, and sure enough, the degree of mechanical disadvantage is huge. Therefore, the force generated by both cylinders together is going to be much greater than the 40-pound force that is actually applied toward lifting your boat. That doesn't mean you might not be able to find cylinders that can lift more than the factory originals. It just means the rating of the cylinders you seek will be a lot greater than what you are thinking. On the other hand, I don't know if the machine is robust enough to handle this extra force. How heavy a boat are you lifting? Once 40 pounds of that weight is taken off your hands, there's not much left. I load a 31-pound canoe overhead and there's nothing to it (all my other boats require special technique to make roof-top loading easy, but the 31-pounder can be loaded "the hard way" and it's still almost effortless). I can't imagine your share of the load will be much worse than that, and what's more, it's being guided and controlled for you too. I'm thinking the factory-original lift capacity should be fine.

One final thought: You say that installing stronger lift cylinders may reduce the problem of "unequal lifting", but I suspect that the opposite will be the case. Think about it this way, if you lifted the whole load yourself, you would make sure one rack didn't rise a whole lot faster than the other. This unequal-lifting problem is caused by the fact that when one rack gets a little "ahead" of the other, the geometry of the device causes mechanical advantage to increase (it's still a mechanical DISadvantage, but now, to a lesser degree). Use cylinders that can't quite lift their share of the load and this problem is easy to control because only YOU can provide that little bit of extra effort to raise the boat. Use cylinders that can easily lift more than what you ask them too, and whichever rack gets just a bit ahead of the other is really going to "take off", and the stronger the cylinders, the greater the magnification of this situation.

 
 
  spring ratings
  Posted by: old_user on Jan-05-13 9:39 PM (EST)
No ratings on the existing cylinders. It was the first thing I looked for. I can't use a scale to determine the rating either because the springs are worn out. Springs are available in this size up to 130lbs.
 
 
  boat weight
  Posted by: old_user on Jan-05-13 9:41 PM (EST)
The boat could weigh as much as 80 lbs.
 
 
  Choosing Spring Ratings
  Posted by: guideboatguy on Jan-05-13 10:01 PM (EST)
-- Last Updated: Jan-05-13 10:12 PM EST --

I suppose the next step might be to see if the folks at Thule will tell you what force is exerted by their cylinders. Odds of success that way are slim though, because they will know in an instant that you intend to buy something from the aftermarket so they aren't likely to tell you what you want to know. But who can blame you for looking elsewhere? Thule will most likely charge you as much as ten-times what equivalent cylinders would cost from an average hardware or automotive-parts dealer, and if that turns out to be the case, they don't deserve your business anyway.

Any chance you can find a fellow paddler with a Hullivator, so you can just remove a cylinder and test it on a scale?

For reasons I already described, my hunch is that you'll want cylinders with load rating toward the high end of what's available, if as you say, the maximum you can get is 130 pounds.

On the outside chance that you are really good with trigonometry, or if you have a friend who is, you can calculate the load rating of the original cylinders by measuring dimensions and angles of all parts of the device when the parallelogram is fully open, where maximum lifting force is provided. Assign a 20-pound force to the direction of lift when the device is in that fully-open configuration and work out the other forces from there.

 
 
  calculations
  Posted by: old_user on Jan-05-13 10:18 PM (EST)
I know a fair number of math teachers. They should be able to figure it out I suppose if they are willing to tackle it.
The problem with using someone else's Hullavator is that the rivets holding the cylinder on will have to be drilled out and replaced with something less aesthetically pleasing.
Replacement cylinders aren't that expensive from MCmaster-Carr--about $24 each with the fittings.
You're right about Thule. Most of their stuff is very expensive and the Hullavator especially. But for people with back or shoulder problems or high vehicles or short people, they are quite useful.
 
 
  rating of gas springs
  Posted by: old_user on Jan-08-13 5:15 PM (EST)
I talked to Thule and they said that each gas spring was rated at 40 lbs. I will probably try 60 lb springs. I'm not that confident that the customer service rep was giving the correct rating of the spring since 40 lbs happens to correspond to what they say the rack will lift.
 
 
  It COULD be correct.
  Posted by: guideboatguy on Jan-08-13 5:39 PM (EST)
We know that the springs need to be a lot stronger than what the rack will actually lift. There are TWO springs, so the total force is 80 pounds, and the rack is rated to lift 40. It's certainly possible that they gave you the right information. I bet it's also possible that you talked to some dummy who knows absolutely nothing about this stuff, and the 40-pound rating was stuck in their head, as you suggest.
 
 
  Yes
  Posted by: old_user on Jan-08-13 6:16 PM (EST)
It could be right. And the number didn't just come immediately to the rep's mind. He left the phone to investigate the question and came back to tell me that Thule does not sell replacement gas springs but a 40lb spring would be needed. So it appeared that someone somewhere was familiar with the problem of failing gas springs on the Hullavator.
 
 
  Update
  Posted by: old_user on Jan-20-13 12:45 PM (EST)
Thule provided inaccurate information. The original springs were clearly not rated at 40 lbs. I bought two 60 lb replacement springs and installed one. The power of a 60lb spring is considerably less than the power of the originals. It takes less than half the effort to 'cock' the Hullavator with a 60lb spring. I've sent an e-mail to Thule with a complaint regarding their information. I was told 40 lbs on the phone and 40lbs in a separate e-mail. It took quite a bit of effort to replace the original spring and I am not happy since I acted on misinformation. I would not recommend that the average DIY or inexperienced person attempt to replace the gas springs. It is a tricky procedure which would result in bodily harm if the compressed spring gets away from you.
My estimate at this point is that the original springs had to be in the 100 lb range or something like that.
 
 
  Liability
  Posted by: Marshall on Jan-21-13 10:34 AM (EST)
I would guess that Thule doesn't want any modifications to the mechanism being done by anyone other than Thule, for the exact potential injury and mechanical complication issues you've mentioned. I don't know how much traction your complaint is going to get.

See you on the water,
Marshall
The River Connection, Inc,
Hyde Park, NY
www.the-river-connection.com
 
 
  Thule
  Posted by: old_user on Jan-21-13 12:59 PM (EST)
Yes, that's probably true. But, I did tell them exactly what the problem was and what I intended to do in replacing the gas springs and that I needed to know the exact poundage of the springs in order to do that. They told me 40lbs.
 
 
  .
  Posted by: suiram on Jan-22-13 9:46 AM (EST)
Not to defend Thule, but 40kg come out at 88lb, which is quite close to the 100lb
 
 
  Thule customer service problem
  Posted by: old_user on Jan-22-13 10:54 AM (EST)
I think their problem is that they think that since the Hullavator lifts 40 lbs, the gas springs must be rated at 40 lbs. It was the same mistake I initially made. But it could be 40kg.
 
 
  Best option
  Posted by: CEWilson on Jan-21-13 11:56 PM (EST)
Instead of spending ~half a K on a hullavator, put that cash into the boat! You can then left your kayak onto the racks and carry it to the water. Neat concept, get a lighter boat.
 
 
  cost of hullavator
  Posted by: old_user on Jan-22-13 9:28 AM (EST)
I've got plenty of boats, many of which are light, but I also am getting plenty of years, so the Hullavator is more appealing. I have a couple of high vehicles and getting any boats up there, light or heavy is an awkward task. Hence my interest in overpriced accessories.
 
 
  Another leverage option
  Posted by: Marshall on Jan-22-13 9:54 AM (EST)
You could always use a Kari-Teck Rolling Rail Rack arrangement. It requires a bit of coordination but I carry 3 kayaks on it in Thule Hull-a-Port Pros on my SUV which is way tall.

Important disclaimer: this device does not make kayaks lighter.

The other option is going to be some trailer arrangement.

See you on the water,
Marshall
The River Connection, Inc.
Hyde Park, NY
www.the-river-connection.com
 
 
  Kerry, We have two Hullivators and
  Posted by: shirlann on Jan-22-13 7:37 PM (EST)
like you we are getting up there in years, plus I am a shorty. Hubby is 5'8". Love my Hullavator. Wish I'd had one years ago, but glad it isn't the earlier style which had problems with the gas struts.
I bought mine at EMS, online when they had a 20% off sale. Absolutely enjoy my Hullavators. I won't give them up until I'm to physically unfit to paddle anymore.
 
 
  Reply from Thule
  Posted by: old_user on Jan-23-13 11:51 AM (EST)
I heard back from Thule. They agreed that their tech department had given the 40lb figure and offered to resolve the problem by shipping me new lifting assemblies with struts.

Kerry
 

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