MacGregorSailors.com

I would love to see video of the captians view and heading directly into 2-3 foot waves... and see if the camera gets wet.

Here's a few more movies, filmed from the bow looking aft while my friend drives. We were outrunning some foul weather. We're going about 13kts. He has a 30' Pearson that was useless today as there was no wind - so I took him out and had to haul home to beat out the rain. He'd never gone faster than his hull speed and was impressed with the dual nature of the Mac

1. TAKE 1

2. Starboard Sm Rail looking aft

3. TAKE 3

4. TAKE 4


It's fairly flat this day, however, that fact doesn't change what the rails do. From the videos you can see from the front how far the rails throw the water away from the boat, producing a dry ride.

I have also been sailing since the rail install. The rails do NOT affect sailing negatively - period. That's because we installed them in a straight line, below the boot stripe.

I just wanted to clearly show what these rails do and have done for me. I don't sell these or profit from it. This is among the best mods I have done. It adds to me and my passengers comfort without encapsulating or shielding us in a way that shows. Everytime I go out I'm dry.

I HIGHLY recommend this mod. Tony's had it for 4 years, problem free; & So long as I installed them correctly, I too look forward to many years of dry boating.

-Gaz

Without exception it appears that all comments and photos regarding the effectiveness of the "smart rail", to prevent waves from riding up the sides, deal with outboard speeds of ten plus knots. My outboard happens to be a 9.9 hp Honda which only provides my Mac with a slightly above normal sailing speed. Would the "smart rail" provide sufficient wave protection at normal sailing speed to justify the cost?

I fixed the links

Has anyone put these on an M?

Have a look at the smart rails setup on my boat.

http://www.youtube.com/watch?v=dORyeg4JIV4

Gaz, and others....

I've contemplated putting rails on my for some time, and it is on my list for next spring when working/gluing temperatures come back up to normal again. Apart from the near elimination of the forward spray from being thrown back, I have an idea that a nine foot section of these could be attached under the hull, running forward from the rudder locations, at the stern. They would run in the water the whole time, with some small drag penalty, and keep the stern of the boat from squatting and interfering with the bow wave when going on plane.
In effect two of them would channel the under-hull water straight back throughout the speed range. Like a low profile pair of keelsons.I wouldn't think the drag would be too pronounced at sailing speeds to be detrimental (?).
They are expensive though (especially if I added them as front spray rails, as well), and I would have to modify the rear trailer bunk to make it work!
I had corresponded with their manufacturer, who thought that it could work, but left it to me to confer with MacGregor over placement and approval of the idea - which ain't going to happen.
Anyone got any input on this idea?

Ross

Hi Ross,

Thinking through the forces involved, it seems to me that you will likely destabilize high-speed steering while on a plane by doing this.

When planing, the stern of the boat is supposed to side-slip in order to keep the thrust vector pointing directly into the turn. If you draw a curve on a piece of paper and then cut out a boat-shaped marker, when sailing the bow and stern of the boat align with the curve through a turn, but when planing the bow stays on the curve while the stern points directly at the next "boat length" of upcoming curve. The stern side-slips outside the curve so that the thrust vector points the boat to where it's going next. Reducing that side-slip reduces the radius of the curve.

The effect of these rails will be a pronounced reduction in roll while turning that at minimum will increase your planing turn radius and if the effect is extreme, it will make the boat unstable in turns. It will also put a considerable amount of lateral force (hundreds to thousands of pounds) on those attached rails, which they may or may not be able to take without de-laminating.

Certainly it will help the boat get up on a plane when going straight, but the boat may "fall off" when turning which will further contribute to instability in a planing turn.

Almost certainly the best place for the stern planing rails is just above the chines, where they will contribute to a "flatter" stern. That both assists in getting on a plane and contributes to proper side-slip while in a turn. I believe it's where the rail manufacturer recommends putting them as well.

Can't believe I never saw this thread, hey these look like a great idea, be even better if they were incorporated in the original hull
Don't have a lot of problems with spray but would be good if heading just off the wind into rough water with any speed you didn't get wet.
At present not looking at putting them on the but have a poly boat that is very wet and was looking to fabricate something just like these, thank you for bringing it to my attention, the fast rails look good too.

Gazmn wrote:Keeping it on a straight line, under the boot stripe works great and doesn't affect sailing.
Here's a pic of the Smart Rail at work; This is mid starboard rail looking forward @ 18kts.

With the 50hp-Suzuki my is making just 12 kts
Do You think with Smart Rails it will go 18kts as well?

Rainer

mastreb wrote:Hi Ross,

Thinking through the forces involved, it seems to me that you will likely destabilize high-speed steering while on a plane by doing this.

When planing, the stern of the boat is supposed to side-slip in order to keep the thrust vector pointing directly into the turn. If you draw a curve on a piece of paper and then cut out a boat-shaped marker, when sailing the bow and stern of the boat align with the curve through a turn, but when planing the bow stays on the curve while the stern points directly at the next "boat length" of upcoming curve. The stern side-slips outside the curve so that the thrust vector points the boat to where it's going next. Reducing that side-slip reduces the radius of the curve.

The effect of these rails will be a pronounced reduction in roll while turning that at minimum will increase your planing turn radius and if the effect is extreme, it will make the boat unstable in turns. It will also put a considerable amount of lateral force (hundreds to thousands of pounds) on those attached rails, which they may or may not be able to take without de-laminating.

Certainly it will help the boat get up on a plane when going straight, but the boat may "fall off" when turning which will further contribute to instability in a planing turn.

Almost certainly the best place for the stern planing rails is just above the chines, where they will contribute to a "flatter" stern. That both assists in getting on a plane and contributes to proper side-slip while in a turn. I believe it's where the rail manufacturer recommends putting them as well.

Thanks for the mental effort Matt! Let me debate a few counter points that you have made.....

The M1000 model that I would have to use, due to the flat bottom, is only one and a half inches into the water. Do you think it would have as pronounced a negative effect in destabilizing turning or 'falling over' itself as you mentioned, at these sizes? Given the fact that very many powerboats operate successfully in this regime with hulls full of chines, wouldn't this just be a little chine?
In a turn under power doesn't the hull lean into the curve, as well as (as you noted) slide, somewhat, around the rotation axis. While a rail may have an impact on these actions, couldn't that also translate into a positive result through enhanced tracking because of the rails?

From what I've read through testimonials, the bonding - if done properly - is pretty industrial! Again, because of the dimensions I can't imagine forces going into the thousand pound range. Though if I'm wrong here it would be a pretty expensive failure.

I don't think, apart from forward spray reduction, which on these boats is a proven issue, that a high rearward placement (near the waterline?) would have sufficient contact to raise the stern much. You can't use the other models because they are made for chine edge attachment - or is too large (and expensive!). Ignoring any possible truth of negative effects in the above discussed regimes, the control of water under the hull would require a more aggressive approach through direct channeling.

Any Macgregor with these currently installed as splash guards must sail heeled with one fully immersed along the hull side. I haven't heard mention of slippage, or pointing, being changed. My gut tells me (though that's not a good basis for argument!) that it should track better using the rail on one side, and probably lessen the weather helm somewhat. Rearward lower mounting - per my idea - should certainly cut the tendency of the stern to swing out so freely while sailing. Whether this would destroy tacking responsiveness is open to conjecture and eventually experiment.
Ixneigh glassed on two rearward skegs forward of the rudders. Not over as large an area as I'm envisioning, but I'm guessing, enough to provide some data about this idea. Maybe we'll get some feedback before long.

Funnily enough I got into this thought experiment by doing some background reading on German WWII Schnellboots (E-Boats) which chose a very similar hull form to the MacGregor. They resorted to a stern end wedge in order to solve the 'squat' (as well as about nine thousand horsepower!). There was also an equivalent forward shaping, similar to the use of a spray rail, to reduce the blowover at the bow.
They also did a very interesting thing with two canted rudders to boost speed in attack conditions (Lürssen Effect).

Of course, all this becomes academic if the Admiral doesn't let me splurge the six hundred bucks I'll need for it, in the spring!

Ross

I believe I understand what your saying and maybe this IS different .. but as a family we have a 20' ski boat. One that was custom built and then modified by Bobby Switzer..( long story) but that boat has "wings" each side of the transom .. to do Just that..... Track.. Very Expensive to incorporate.. maybe the only boat out there with them, outside a few race boats ( hence Bobby Switzer Off Shore Race Team) Those. these .. boats slide VERY Little.. They dig and point.. any speed.. YES... it can be very dangerous .. but not a flipping situation.. just he G force exerted on the driver and occupants.. But NO Doubt.. a HUGE differences between Our Boats versus a Low Long Wide Ski Boat..with a 1/4 turn of the wheel at 60mph that boat slides very little The wing, digs in and its like you being SHOT from a cannon.. The Inertia is incredible but it runs true and stable.. If.. you can hold on and stay in the seat.. Hence the 4 point harness for the driver..
**** So I ASK ? Is it our huge free board? Center of Gravity? etc etc etc.. that would make the difference?

mastreb wrote:Hi Ross,

Thinking through the forces involved, it seems to me that you will likely destabilize high-speed steering while on a plane by doing this.

When planing, the stern of the boat is supposed to side-slip in order to keep the thrust vector pointing directly into the turn. If you draw a curve on a piece of paper and then cut out a boat-shaped marker, when sailing the bow and stern of the boat align with the curve through a turn, but when planing the bow stays on the curve while the stern points directly at the next "boat length" of upcoming curve. The stern side-slips outside the curve so that the thrust vector points the boat to where it's going next. Reducing that side-slip reduces the radius of the curve.

The effect of these rails will be a pronounced reduction in roll while turning that at minimum will increase your planing turn radius and if the effect is extreme, it will make the boat unstable in turns. It will also put a considerable amount of lateral force (hundreds to thousands of pounds) on those attached rails, which they may or may not be able to take without de-laminating.

Certainly it will help the boat get up on a plane when going straight, but the boat may "fall off" when turning which will further contribute to instability in a planing turn.

Almost certainly the best place for the stern planing rails is just above the chines, where they will contribute to a "flatter" stern. That both assists in getting on a plane and contributes to proper side-slip while in a turn. I believe it's where the rail manufacturer recommends putting them as well.

As for having them near the waterline, when powering the wake lifts above the waterline, having these speed rails at that location uses the upward force of the wake to lift the boat. That's why they're a bit of a freebie: No effect when you're below hull speed because they're out of the water, but a reduction in drag when powering because they're being lifted by the wake.

It's really hard to determine exactly how much effect the speed rails will have under the hull. All I can say is that it will be something between what it is now and zero side-slip. If the improvement in reducing squat is much greater than the reduction in turn radius, then it'll be a big win.

I would try to make sure that the placement of the rails is such that one will come out of the water in a high-speed turn. That will cut the roll reduction effect in half. Directly in-line with the rudders seems like the right place.

There won't be any negative effect to sailing except a minor amount of additional drag--considerably less than leaving the motor in the water. In fact it will almost certainly be an improvement in reducing leeward side slip and in pointing correctly during a tack. These boats are really loosey goosey when tacking because of the stern side-slip that is necessary for powering. Skegs will definitely improve that.

You're going to have to test to determine whether the potential negative is worse than the positive. I'm not all that interested in powering so this is a mod I may do myself if it improves steerage while tacking.

You'll also have to be careful about how these trailer and ensure that they don't hit the bunkers sideways when you're coming onto the trailer. I'm sure they'll be applied while on the trailer so that shouldn't be an issue.

Divecoz wrote:I believe I understand what your saying and maybe this IS different .. but as a family we have a 20' ski boat. One that was custom built and then modified by Bobby Switzer..( long story) but that boat has "wings" each side of the transom .. to do Just that..... Track.. Very Expensive to incorporate.. maybe the only boat out there with them, outside a few race boats ( hence Bobby Switzer Off Shore Race Team) Those. these .. boats slide VERY Little.. They dig and point.. any speed.. YES... it can be very dangerous .. but not a flipping situation.. just he G force exerted on the driver and occupants.. But NO Doubt.. a HUGE differences between Our Boats versus a Low Long Wide Ski Boat..with a 1/4 turn of the wheel at 60mph that boat slides very little The wing, digs in and its like you being SHOT from a cannon.. The Inertia is incredible but it runs true and stable.. If.. you can hold on and stay in the seat.. Hence the 4 point harness for the driver..
**** So I ASK ? Is it our huge free board? Center of Gravity? etc etc etc.. that would make the difference?

It's the rounder hull on a mac that makes the difference. I'm guessing the stern of your ski boat is very nearly square and flat. That hull shape produces a considerable resistance to any kind of rolling--the "side buoyancy" is much higher than our rounder hulls and comparable to a catamaran of similar width. Without that kind of flatness resisting roll, the G-forces in a turn are converted to an outside roll, which is where the flipping danger comes from.

Consider that if you power a mac with the daggerboard down and try to perform a power turn, the boat will do an outside roll and capsize. That's the maximal version of the effect I'm talking about. Any amount of hydrodynamic resistance to rolling, even the stock chines on our boats, reduces inside roll and contributes to outside roll. The only question is "how much resistance is too much" and whether the positives outweigh the negatives in sum.

mastreb wrote:As for having them near the waterline, when powering the wake lifts above the waterline, having these speed rails at that location uses the upward force of the wake to lift the boat. That's why they're a bit of a freebie: No effect when you're below hull speed because they're out of the water, but a reduction in drag when powering because they're being lifted by the wake.

Except, at this location the water stream under the hull has already dispersed laterally, by displacement, before it can impart its energy to the rail. The friction penalty would still exist as a percentage of a fully immersed rail. Being higher before suddenly interacting while heeling may be undesirable compared to steady state running.

mastreb wrote:I would try to make sure that the placement of the rails is such that one will come out of the water in a high-speed turn. That will cut the roll reduction effect in half. Directly in-line with the rudders seems like the right place.

I've never actually cranked it hard under power, yet! So I don't really know what the inboard lean would be under WOT as a max case. A power turn gives you an inboard lean of some degree, and I can't determine if there would be enough, in this location, to fully get it clear of the waterline. Sailing - yes, power - uncertain?

mastreb wrote:There won't be any negative effect to sailing except a minor amount of additional drag--considerably less than leaving the motor in the water. In fact it will almost certainly be an improvement in reducing leeward side slip and in pointing correctly during a tack. These boats are really loosey goosey when tacking because of the stern side-slip that is necessary for powering. Skegs will definitely improve that.

I'm thinking of it in the same sense as a wing fence on an aircraft. Except it's water, not air (and I can still beach it!).

Ross