The Macgregor bump

[stepfour]

I was wondering why nobody talks about the Macgregor bump? I just bought a 1994 Macgregor 26S and absolutely love it. There was one thing I was having a problem with, loading it all the way on the trailer. it didn't matter what i did i could not get it positioned correctly in the V. I would get in all the way up but as soon as i pulled it out the bow would lift up and now i would have a 6" gap. One day someone told me about the Macgregor Bump. load the boat get drive about 10 mph and tap the brakes. Boom it worked perfect. I don't want to hurt my boat or mast. Where i keep it i keep the mast up because there is nothing over head from the parking spot to the landing. Would this hurt my mast? any thoughts or concerns would be great.

[Russ]

First, welcome to the forum and we are glad to have you post questions.

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[pitchpolehobie]

Somebody did report they did the mac bump and it jumped to the side of the roller and into the back of their tow vehicle. That seemed inconsistent with the amount ot force and finesse Ive applied to the manuever but id probably take that into consideration. ymmc.

[Be Free]

Personally, I would not do the "bump" with the mast up. I used to do it early on but I started worrying about all those forces involved and that 30' lever sticking up off the top of the boat.

Even a lightly loaded boat is going to be somewhere north of 3000 pounds on the trailer. At 10mph that's over 10,000 ft pounds of kinetic energy that is going to have to go somewhere in less than a second. Hopefully all that happens is a gentle bump against the bow roller.

[kurz]

If You have a second person he can pull the trailer winch in that time when you go up the ramp. Then you don't need thee bump, because the boat gets at the right place.

[Stickinthemud57]

I'm with BeFree. Not with the mast up.

I usually don't have help at the ramp, so the "bump" is just part of the process. With a lightweight boat like the 26S it's no big deal. I would say 5 mph or less, though.

[Jimmyt]

Not a Mac bump guy myself, but wondering if the load on the shrouds is any higher when Mac bumping vs being in a 15-20 kt breeze under sail in pounding surf. Haven’t crunched the numbers, but?

Sumner had my favorite solution. Hasn’t made it to the top of my list yet, but it’s on there.

viewtopic.php?p=315755#p315755

[Be Free]

Not a Mac bump guy myself, but wondering if the load on the shrouds is any higher when Mac bumping vs being in a 15-20 kt breeze under sail in pounding surf. Haven’t crunched the numbers, but?

Sumner had my favorite solution. Hasn’t made it to the top of my list yet, but it’s on there.

viewtopic.php?p=315755#p315755

Jimmy, I'll trust your numbers over mine if you ever get around to crunching it. I was a physics major on my way to MIT when I did an about face and went to UF for Wildlife Ecology. My calculus is almost as rusty as my trig and I've not made a living with either in a very long time.

I suspect the forces are significantly higher on the trailer than in your hypothetical though. The suggested 10mph on the trailer would be over 8.5 knots which you could theoretically get with 15-20 knots of wind behind you and conditions were perfect but you would be catching up to the waves and/or surfing them so you would not be hitting them and pounding. I can't imagine any Mac sailing 8.5 knots into the wind let alone doing it while pounding into oncoming waves.

My main concern with doing the bump with the mast up not what happens if you do it exactly right, i.e. the boat uses up all that kinetic energy as it gently nestles into the bow roller. My concern was what would happen if the boat stops suddenly with a portion of that energy still in play. My back-of-the-envelope calculation showed deceleration forces of several Gs could easily be generated. It was more about the potential shock loads on the rigging and their associated fittings that made me stop "bumping" with the mast up.

[Jimmyt]

The suggested 10mph on the trailer would be over 8.5 knots which you could theoretically get with 15-20 knots of wind behind you and conditions were perfect but you would be catching up to the waves and/or surfing them so you would not be hitting them and pounding. I can't imagine any Mac sailing 8.5 knots into the wind let alone doing it while pounding into oncoming waves.

My main concern with doing the bump with the mast up not what happens if you do it exactly right, i.e. the boat uses up all that kinetic energy as it gently nestles into the bow roller. My concern was what would happen if the boat stops suddenly with a portion of that energy still in play. My back-of-the-envelope calculation showed deceleration forces of several Gs could easily be generated. It was more about the potential shock loads on the rigging and their associated fittings that made me stop "bumping" with the mast up.

All great points. I’m thinking more combined wind load on the sail and pounding. But, as I said I haven’t crunched numbers. I’ve also had some rather dramatic high wind gybes that I thought should have brought down the rig (my racing buddies do a lot of gybing to keep the boat speed up - even when they aren’t racing).

I will absolutely agree with you, though. Bumping at 10 mph, with the rig up (or even with it down) is way out of my comfort zone. I’m not even sure that the winch mount is strong enough to stop the boat if the trailer and tow beast do a quick stop from 10 mph. Stopping a 100 pound mast suddenly is one thing. A 3,500 lb (or higher) boat is a whole nuther kettle of fish.

Does anyone actually bump that fast? If so, are you locking the brakes until stopped, or just making a rapid momentum change to a lower speed?

Always a fun thread when bumping comes up. It is not just a Mac phenomenon, either. I’ve read several threads on other forums where various trailer boat owners were debating the wisdom of bumping.

[Be Free]

I got the 10mph example from the OP. I don't know how fast I get up to. I've never looked at the speedometer but I lock the brakes at whatever speed it is. The ABS on the tow beast kicks in but the trailer brakes don't have that option; all four wheels are locked. Even so it can take three or four passes to get the boat where want it.

The wind load on the sails should all be within design specs. Main and jib should be about 280 square feet and I would hope that the rigging was designed to take anything that 280 square feet of sail can throw at it. Upwind the boat will round up. With the wind on the beam it will heel and reduce the wind forces. Downwind the main concern would be any type of uncontrolled gybe but that is more of a danger to the crew and the boom fittings.

Pounding into the waves going upwind is going to produce shock loads to the rigging and fittings but again I would hope that those conditions were allowed for when the boat was designed. We are not like your friends' race boats. We are too light to put up with much wave action without slowing down a lot. We are too heavy in relation to our sail area to get up much speed from one wave to the next anyway.

Personally, I'm not going to bash my way upwind for long under sail in a large chop and I suspect that I'm more willing to do that than most. I ripped the clew out of a perfectly good jib doing that and I don't like sewing enough to do it again.

I don't know about the other models, but the X cockpit gets very wet under those conditions. Shock loads aside, it seems like every wave you hit lands directly on the helm seat.

[NiceAft]

I don't know about the other models, but the X cockpit gets very wet under those conditions. Shock loads aside, it seems like every wave you hit lands directly on the helm seat

That, and other conditions. Now you know why Mac’s are know as “Wet Boats.”

[pitchpolehobie]

The suggested 10mph on the trailer would be over 8.5 knots which you could theoretically get with 15-20 knots of wind behind you and conditions were perfect but you would be catching up to the waves and/or surfing them so you would not be hitting them and pounding. I can't imagine any Mac sailing 8.5 knots into the wind let alone doing it while pounding into oncoming waves.

My main concern with doing the bump with the mast up not what happens if you do it exactly right, i.e. the boat uses up all that kinetic energy as it gently nestles into the bow roller. My concern was what would happen if the boat stops suddenly with a portion of that energy still in play. My back-of-the-envelope calculation showed deceleration forces of several Gs could easily be generated. It was more about the potential shock loads on the rigging and their associated fittings that made me stop "bumping" with the mast up.

All great points. I’m thinking more combined wind load on the sail and pounding. But, as I said I haven’t crunched numbers. I’ve also had some rather dramatic high wind gybes that I thought should have brought down the rig (my racing buddies do a lot of gybing to keep the boat speed up - even when they aren’t racing).

I will absolutely agree with you, though. Bumping at 10 mph, with the rig up (or even with it down) is way out of my comfort zone. I’m not even sure that the winch mount is strong enough to stop the boat if the trailer and tow beast do a quick stop from 10 mph. Stopping a 100 pound mast suddenly is one thing. A 3,500 lb (or higher) boat is a whole nuther kettle of fish.

Does anyone actually bump that fast? If so, are you locking the brakes until stopped, or just making a rapid momentum change to a lower speed?

Always a fun thread when bumping comes up. It is not just a Mac phenomenon, either. I’ve read several threads on other forums where various trailer boat owners were debating the wisdom of bumping.

Ive also just not moved it when its already 3 to 4 inches from the bow touching the pulpit. I put a stern strap and after 100mi it hasnt budged.

[Be Free]

I'm not worried about it moving. I've noticed that if it's even an inch or so from the roller I start to fishtail above 50. I need it all the way into the roller to get my tongue weight where it needs to be.

[Jimmyt]

…I've never looked at the speedometer but I lock the brakes at whatever speed it is. The ABS on the tow beast kicks in but the trailer brakes don't have that option; all four wheels are locked. Even so it can take three or four passes to get the boat where want it.

That must be a real conversation starter at the ramp.

If the ABS is activating, you’ve got at least one wheel broken loose. Is that on dry pavement, or dirt/gravel?

I don't know about the other models, but the X cockpit gets very wet under those conditions. Shock loads aside, it seems like every wave you hit lands directly on the helm seat.

My M doesn’t seem to be that bad. It’s not as dry as the island packet 31 with dodger and huge Bimini; but it’s a whole bunch dryer than the fish boat - where everyone gets wet beating into a chop.

…I can't imagine any Mac sailing 8.5 knots into the wind let alone doing it while pounding into oncoming waves.

I can confirm that I have never sustained 8.5 kts under sail at any point of sail - not even close when beating into a big chop.

Good stuff.

I’ve never had a problem towing with the boat being a few inches out of the v-block. But, I have the factory aluminum single axle trailer. My boat is likely not as heavy as most.

The boat being snug in the v-block does add some rigidity to the front end of the trailer, though. It definitely flexes more when the boat is not tight in the v-block.

[Be Free]

Jimmy,
There are only about 500 full-time residents here but we have 2-3 times that on most weekends and several thousand people here if there is something special going on.

Since I'm semi-retired I try to plan my launching and retrieving to be on days when the ramp is not heavily used. If there is even one other boat at the ramp I consider it busy. I've gotten some comments when I pull the ballast valve after getting the boat on the trailer and a few strange looks while doing the bump but never any comments.

The area at the top of the ramp is paved but it usually has enough gravel and debris on it that the wheels will slide.

I have an aluminum dual-axle trailer and my boat is definitely on the heavy side. I don't remember the last time I did a day sail. I'm usually out for at least 4 days any time I launch.