Mac 'bump' and silicone

[Steve K]

I was thinking it was a good stretch.
SK

[JohnWood]

Is the bump even needed?

I'm a new owner of a 91 Mac 26S. When I bought it, the boat sat on the trailer a few inches off the bow bumper. I drove it that way from New Orleans back home to Largo, Fl. I did add one extra rope from the bow eye down to the tongue. Each time I've pulled it out of the water, I just let it be a few inches back. Tongue weight seems to be around 150#. Is the bump mentioned anywhere in the manual? If bow is tied securely, there is sufficient tongue weight, and there is a strap or rope over the mid/rear of the boat, what is the compelling need to do the "bump"?

[seahouse]

There is none in some cases, such as your's and mine, John. It meets all the requirements of a trailer, is totally secure and safe, and might even be an improvement in weight distribution (my case, the tongue was on the heavy side of the range to start) but there are almost certainly some exceptions, too.

Contrary to what some might think (and have posted here), the rubber "V" bumper does not secure the bow from sideways movement on our (M at least) boats. At all. This is easily demonstrated by pulling on it sideways with your hand when it is not in contact with the hull; it's very flexible, and simply results in torsion being applied to the tongue. For the same reason, in fact, that the torsion bar that is in the suspension of the trailer itself is such an effective cushion. (It is more the reverse that is true, it is in fact the hull that secures the rubber "V" block from sideways movement).

That function is instead performed (on the "M" trailer at least) by the V-shaped bunk mounted on the trailer tongue aft of the upright, which securely captures and engages the hull even when it is back several inches from the rubber stop, and prevents sideways motion of the bow on the trailer. If the U bolt in the bow is secured to the upright by both the winch and a redundant method (such as a rope) it will hold the bow downward and into that V-bunk, preventing movement. (Adding a lubricant would reduce that effect, undesirable for me). The two work together to prevent movement.

Of course, if catastrophic forward movement (collision) overcomes the sum of the other hold-downs, the rubber V-block is still in position to contribute. The upright and rubber V also perform the minor function of a reference datum point where the boat should stop relative to the trailer so that the position, and thus the weight distribution, is repeatable.

In my case the friction of anti-foul on the bunks prevents the Mac bump from budging the boat at any reasonable speed, even with the winch strap rerouted and pre-tensioned so as to pull upward on the bow to reduce the contact. After studying it I came to the same realization that you have John; if it's all secured as it should be, and weight distribution is within tolerance, that's all that counts. That could be easily demonstrated to an MTO inspector who might happen to inspect and question it, although being legal is a secondary priority to me to being safe, but both bases are covered.

- B.

I will make the following update. As I have pointed out before, the hull provides structural support to the trailer, making the two function together as a single solid unit.
While as mentioned above the rubber V does not steady the boat, the hull will have a steadying and supporting effect on the trailer when the rubber V is engaged to the hull. While it is a small detail that does not apply to most, I mention it for those few to whom it does apply. In the interest of good form, when I pulled the boat for the season I fabricated a carpet-covered tapered 2 X 4 on edge and used it to fill the gap between the V and the bow, securely held in place by a cable tie should it come loose, and by tightening the winch down onto it.

[sagehill]

Seahouse has made many good points. I also believe that the 26M sitting aft yields better weight distribution on the single axle. I pack all the luggage in the rear bunk for trailering, but redistribute the load on the water. As a professional engineer, the design of the 26M aluminium trailer winch and bump stop has irked me to no end. Like others, I have considered re-welding the winch above the bump stop to get the lifting action on the bow eye but the resulting pitch is not enough to keep the bow in contact with the bump stop once the stern sits down onto the trailer. Hard winching pulls the boat forward (some) but it also induces undesirable (additional to road flex of the trailer) tension on the bow eye as well as torsion into the trailer's aluminium beams. One possible workable solution is to re-mount the bump stop like a tow ball, with a sliding shaft (tow ball mount) and a receiver. With multiple pin hole for variable adjustment, the sliding bump stop can now be moved back to contact the bow of the boat after the boat is seated on the trailer. This solution has the advantage of helping with the weight distribution aft, however note that the new contact point of the bow with the V-bunk has moved, albeit only by a few inches.
Let me also me mention that like some previous contributors, I too have enjoyed the onlookers during my Mac bump stop days in Canada where the parking lots were asphalt and my tow rig (98 F-350 crew cab long box dually) didn't have front ABS and wet brakes. Bump stops are now impossible for me as I now live in New Zealand where a loose gravel surface is the norm (even the state highways are tar sealed - pebble-sized gravel over sprayed liquid bitumen) and my tow rig (a most excellent Land Rover D3 or LR3) will NOT allow an abrupt stop.
And as this is the trailering and towing forum, I would be remiss to not mention for your consideration, the behaviour of a vehicle with automatic rear self levelling on the ramp - vehicle tail auto raises to self-level, tow bar raises, V-berth gets lifted higher out of the water, the trailer pitch angle is greater than the ramp steepness, vehicle might detect the added load of the boat on the V-bunk and further compensate, vehicle has to wade in even deeper, water at the door sills, etc. Let me mention that I do try to empty my ballast to minimise draft, and I ask sailors to move aft.
Good discussion guys.

[raycarlson]

I added a second bow eye 12 inches lower right at the black stripe, for purposes of boat ramp loading only, so winch pull direction was upward lifting on bow eye while pulling boat up to bow stop roller. In short it still did not stop the necessity of the mac bump, the best thing so far has been the discovery of Liquid Rollers bunk spray. No more jamming on brakes making everyone look in your direction wondering what the hull is that idiot doing..... Just a smooth quick stop, no skidding of tires and the boat slides right up into bow roller.

[Highlander]

There is a simple mod for this someone on this site posted just two eyestraps mounted on the V block hardware then a bolt with a metal tube to act as a roller mounted underneath run the strap up through that & u r now puling the bow eye up & forward

J

[Hamin' X]

There is a simple mod for this someone on this site posted just two eyestraps mounted on the V block hardware then a bolt with a metal tube to act as a roller mounted underneath run the strap up through that & u r now puling the bow eye up & forward

J

Try here: http://www.macgregorsailors.com/modt/in ... ?view=1430

And another mod here: http://www.macgregorsailors.com/modt/index.php?view=547

~Rich

[Highlander]

See ! Ya gotta like these Moderator guy,s

J

[jimbo]

Another forum I frequent suggest that shade cloth over the bunks is far more slippery than the stock bunk carpet.
Anyone tried this?
Will be some weeks before I get a chance.

[beene]

There is a simple mod for this someone on this site posted just two eyestraps mounted on the V block hardware then a bolt with a metal tube to act as a roller mounted underneath run the strap up through that & u r now puling the bow eye up & forward

J

Try here: http://www.macgregorsailors.com/modt/in ... ?view=1430

And another mod here: http://www.macgregorsailors.com/modt/index.php?view=547

~Rich

Thanks Rich

I like that idea better than the Mac bump

My carpets get ripped off when I do the bump a few times

Not to mention I scare the crap out of everyone around when I hit the brakes and Pegasus goes flying fwd on her trailer....

G

[Jeff L]

Can the silicon spray mentioned be gotten at West Marine ? What brand name ?

[Tomfoolery]

Can the silicon spray mentioned be gotten at West Marine ? What brand name ?

http://www.westmarine.com/buy/marikate- ... s--1244805

[Catigale]

you have to watch for sharknados...Shirley, all together..

[Jeff L]

Can the silicon spray mentioned be gotten at West Marine ? What brand name ?

http://www.westmarine.com/buy/marikate- ... s--1244805

Thank you

[Catigale]

Jeff - you can get his at about 1/3 the price at a hardware store compared to WM