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Boat Lift Math........

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    Posted: June-10-2019 at 7:13am
We remodeled our dock and with it came new overhead, cradle boat lifts. The new lifts are PAINFULLY slow. So slow that I had to do something about it. I replaced the 2" diameter pulley on the motor with a 3" pulley. The 10" pulley on the gearbox remains the same. The speed is noticeably better.

I know that increasing the motor pulley diameter increases the rotational speed of the gearbox making that faster (I figured it's a circumferential distance of the different smaller pulleys over time relationship.) What I can't quite set up is the relationship of how I have decreased the lifting capacity of the lift by changing the motor pulley. I can't set up the equations. I don't think it's much but now that Val has time on her hands, she wants confirmation we are Ok to put most any Correct Craft in the lift.

So what is the new lifting capacity with a 3" drive pulley when the old max capacity was 10,000# with a 2" drive pulley? Please show your work....(cuz I can't)   



Click For Full-Size Image.

PS. otherwise, we LOVE the new setup. We have Gem remotes on the lift so we can lower and raise the lift from the boat, the water and the house - great for getting handicapped folks into and out of the boat easily!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 7:34am
Steve,
The lift capacity remains the same. For the given weight of the load, the torque through the worm and spur gears stays the same.


Now the potential problem is the FLA (full load amps) of the motor. I highly recommend you check it against what's listed on the motor nameplate before you burn it up! Is the motor thermally protected? If so, that may save you from damaging the motor.

Clamp on:



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Post Options Post Options   Thanks (0) Thanks(0)   Quote Air206 Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 7:47am
Thermal protection? Beyond GFCI? How does FLA change? By what proportion? Are you suggesting it is a considerable change or a negligible change? Do I clamp on at the switch or motor side? At the breaker box is easiest....... so many questions..........
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Orlando76 Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 7:59am
Both, motor side and breaker side and compare the difference. When I say breaker side, I mean where it originates at the house, I suspect a noticeable difference there. But I don’t expect much difference in motors fla. never really thought about that before.... And for the sake of everyone make sure the ENTIRE circuitry going to the dock is GFIC protected, not just at the receptacle/device itself.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 8:09am
Steve,
Thermal protection consists of a switching device close to or in the motor windings that opens the circuit stopping the motor when heated such as during a motor overload. The nameplate on the motor will state if it's got thermal protection. Sometimes they work and sometimes not since the device isn't very accurate. It is not a GFCI as it simply opens when there's a current fault to ground.

Calculating an increase in motor amps isn't easy since amperage with given motor loads is not linear. That's the reason I recommended checking the actual amps with a clamp on. You clamp the ammeter onto ONE wire anywhere between the breaker and the motor. Since the breaker panel is easily accessible, then clamp it on the load side wire on the breaker.

Now, if you do get a FLA reading over nameplate, then it's time for a new motor with a higher HP.

Off hand, I'd say you will be OK since your lift is sized for 10,000lbs and your boat isn't that heavy.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 8:13am
Originally posted by Orlando76 Orlando76 wrote:

Both, motor side and breaker side and compare the difference. .

Todd,
You won't see a difference in amps from the breaker end to the motor end. I feel you are thinking voltage drop. For the given drop in voltage due to load wire size and length of wire, the amps stay the same.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Air206 Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 8:22am
Originally posted by Orlando76 Orlando76 wrote:

Both, motor side and breaker side and compare the difference. When I say breaker side, I mean where it originates at the house, I suspect a noticeable difference there. But I don’t expect much difference in motors fla. never really thought about that before.... And for the sake of everyone make sure the ENTIRE circuitry going to the dock is GFIC protected, not just at the receptacle/device itself.


Yep - no issues with GFCI it is everywhere at the dock. Also, we test at the open and close of the season..... as they do fail.

When you say noticeable difference - you mean before and after pulley change? Or on one side vs another? (Cuz I am NOT changing the pulley back!)

PS Todd - wanna come to look when you are at SML?   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 8:31am
Steve,
I assume you purchased a longer V belt after putting the larger sheave on the motor. Hopefully you got an AX belt (cogged) and didn't just get a 4L fractional HP belt at the hardware store.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Orlando76 Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 8:37am
Originally posted by 8122pbrainard 8122pbrainard wrote:

Originally posted by Orlando76 Orlando76 wrote:

Both, motor side and breaker side and compare the difference. .

Todd,
You won't see a difference in amps from the breaker end to the motor end. I feel you are thinking voltage drop. For the given drop in voltage due to load wire size and length of wire, the amps stay the same.


Back up Pete and rethink that.... the amps will go up.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 8:39am
Originally posted by Orlando76 Orlando76 wrote:

Originally posted by 8122pbrainard 8122pbrainard wrote:

Originally posted by Orlando76 Orlando76 wrote:

Both, motor side and breaker side and compare the difference. .

Todd,
You won't see a difference in amps from the breaker end to the motor end. I feel you are thinking voltage drop. For the given drop in voltage due to load wire size and length of wire, the amps stay the same.


Back up Pete and rethink that.... the amps will go up.

Todd,
Yes, the amps go up with the voltage drop but what I'm saying you will get the same amp reading at the breaker or the motor end. Maybe I misunderstood what you were saying?


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Orlando76 Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 8:40am
Originally posted by Air206 Air206 wrote:

Originally posted by Orlando76 Orlando76 wrote:

Both, motor side and breaker side and compare the difference. When I say breaker side, I mean where it originates at the house, I suspect a noticeable difference there. But I don’t expect much difference in motors fla. never really thought about that before.... And for the sake of everyone make sure the ENTIRE circuitry going to the dock is GFIC protected, not just at the receptacle/device itself.


Yep - no issues with GFCI it is everywhere at the dock. Also, we test at the open and close of the season..... as they do fail.

When you say noticeable difference - you mean before and after pulley change? Or on one side vs another? (Cuz I am NOT changing the pulley back!)

PS Todd - wanna come to look when you are at SML?   


Let me rephrase that, do you have GFIC breakers installed? I’d love to pick apart somebody else’s electrical work. Seems like my trips to SML keep fading away. When I go I want my boat and camper, that’s what I work for. She wants to leave the camper and stay at her parents..... to hell with that.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JoeinNY Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 8:41am
So yeah Pete is generally correct here in that the lift capacity has not changed from the 10k, however you are using the motor that was sized for the 10k in a different way. Now checking amps and yadda yadda would be what would be needed if you were actually lifting 10k - which you aren't unless your new G25 showed up since we talked last.

If you want to answer the question that your wife is really asking -

So as stated above - nothing is going to break in terms of cables, gear drive, etc. up to the original rating.

For the motor it is running basically the same speed it was always running - and was presumably adequately sized for the load that the gear box would put on it with a 10k boat. we don't know what that load is but lets assume it is x. If we don't want to tax the motor any more than the manufacturer intended ( which again is what Val wanted to know) then we would not want to apply more torque on the motor than we would at x.   You changed the pulley radius from 1" to 1.5" effectively increasing the torque at x by a factor of new radius (1.5) divided by old radius (1) give you 1.5 times the torque at x. Neglecting things that are reasonably neglected here you can simply divide the original rating of the hoist by the 1.5 (10000/1.5) and as long as you are only lifting 6666.7 lbs that motor doesn't know the difference between that and lifting 10000lbs with a 2 inch pulley.

If you lifted 10000 lbs with the 2 inch pulley and measured the FLA and then measured 6666.7 lbs with the 3 inch pulley they would be the same... but just measuring the same 3400 lb ish boat twice at both pulley sizes won't tell ya a whole lot cause neither scenario would really be fully loading the motor as god and the original specifying engineer intended.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Orlando76 Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 8:46am
Originally posted by 8122pbrainard 8122pbrainard wrote:

Originally posted by Orlando76 Orlando76 wrote:

Originally posted by 8122pbrainard 8122pbrainard wrote:

Originally posted by Orlando76 Orlando76 wrote:

Both, motor side and breaker side and compare the difference. .

Todd,
You won't see a difference in amps from the breaker end to the motor end. I feel you are thinking voltage drop. For the given drop in voltage due to load wire size and length of wire, the amps stay the same.


Back up Pete and rethink that.... the amps will go up.

Todd,
Yes, the amps go up with the voltage drop but what I'm saying you will get the same amp reading at the breaker or the motor end. Maybe I misunderstood what you were saying?


Nope. Pete, how long is the feeder going to your dock? I’ll bet 300’? Maybe we are on different pages, but, Operate boat lift and take current reading closest to lift motor. 6a at 240v? Now go back to the house and check it with motor going same direction and it will be drawing more current, unless you’re at like a #4 or larger wire. But #8 or less and there will be more current draw at the house.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Air206 Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 9:17am
I knew this was the mental gymnastics we all would love........

Yes. GFCI breakers - GFCI on the motor, GFCI on the dock outlets. Kids wear belts at the dock.... Mr. and Mrs. Safety here .........along with ridiculous Shoreline Management inspection requirements.

As far as visiting parents, only one survives and I wish our kids could have been around them more when the kids were young and they were alive.......

Thanks, Joe - I was thinking a proportional approach would help with perspective (as it did for motor speed increase).

As far as changing belts, there is easily enough wiggle room to go to a 3-inch pulley with the same mounting plate and belt.

The G25 is the next purchase. I rode a trick ski behind PN Jeff's at WL and got an incredible adrenaline rush just getting up single! Val is shooting for a pontoon, but we can sit more on a G25...... and I always wanted a third mortgage.   
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: June-10-2019 at 10:23am
I'm kinda simple minded but I agree with Joe   

My simple minded equation was               2/3 equals (X) /10000

And X was about 6666 in my head (with the motor doing the same amount of work)
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