Powering with full ballast

[Randy Smith]

BK, you are talking about the older models like my 96. There is a small amount of area which doesn't fill right away....but with "burping" and "side to siding" the boat she will fill. This is superfilling....not necessary past 97. Waternwaves is right, when the tank is full it has become part of the hull and has integrity. I have examined my tank. We are not talking small joints of fiberglass or hollow areas unmolded. The tanks are a part of the boat.....integral to the hull.....not appendages. I do not understand your comment about not going over 6mph with full tanks???? What?? I am on the water all the time, in all conditions....never broken anything or developed problems with the tanks. Must run Macs with full ballast or empty....no partial...very dangerous.
Guys, Roger is the designer, the final stamp.....my friend Bob is a dealer and has gone to the factory many times. Roger hires some very fine and credible engineers, he tells them what his ideas are and they crank out the possibilities. He couldn't carry insurance riders if not.....With the Man's MBA came some pretty good common sense...though over the years some of his final boats, I have said WHAT? Ex. I was not a fan of the 2004M, but love the 2005M('cept for the head)....yup, they be different, slightly ... Remember water ballast has been used for a long time in Europe. Roger is the first to put it to a motorsailor. Y'all remember that top end racers all use water ballast technology for stability. High speed pumps move water to the right places at an incredible rate...out too....they use it for tuning the ride and heel........since 96X's, there has only been the one crack up on the Great Lakes right? We all figure that was to the captain's negligence? Too many people and no water ballast? The design works, and we would know by now wouldn't we? Randy

[baldbaby2000]

One can make the argument that parts of the hull bottom are stressed less when the ballast is full when the bottom of the boat impacts the water. If a wall of water hits a bulkhead and there is water, a non-compressible fluid, on the other side, the mass of that water on the other side will tend to keep the bulkhead from flexing in contrast to the case where there is air, a compressible fluid, on the other side of the bulkhead. Of course there are forces being transferred to other parts of the boat too.

[BK]

Sorry to keep beating this drum but something interesting turned up. Dave Clark and I were looking at new inflatables and the salesman asked what kind of boat we have. He said he did the first speed testing on the Mac X and he got the boat to 21 MPH with a 50HP 2 stroke. They looked at the problem of draining water from the heavy ballast as problem to the life of the engine, not to the boat. He said the rods of the 2 strokes were under the most strain when dumping water from the ballast. The 4 strokes bearing were under the most strain when dumping water from the ballast. So, as I understand his testing, the boat's engine is under the greatest strain with a full ballast at speeds needed to drain the ballast, which makes sense.
If they feel that just the 8-10 minutes of draining the ballast is a strain on the engine, what is running the boat with full ballast at high speed for long periods doing to the 2 or 4 stroke engine?

[Don T]

Hello:
In answer to the gelcoat crazing. My boat is a 95 (tohatsu 50) and there are crazed areas in the hull gelcoat around where the galley and aft dinette seat / head are attached as well as around the centerboard bunk. These hard points are at the apex of the crazing. I noticed it the first year and it doesn't seem to have gotten any worse. Last summer we were out in 5~6' seas which launched us, pounding down into the troughs. It was the last time the boat was out but I have to say I'm worried about hull integrity. I won't know until I get it out next spring. Actually I consider the boat pretty tough but there are those lingering doubts.

[Randy Smith]

BK, the only two years there was a bubble in the water ballast tanks after filling, was 95 and 96. Those boats will fill all the way given a few minutes and proper "burping"(a side to side movement by my 250lb body and she'll fill). Even then, as waternwaves said, the water essentially becomes a solid when the tank is filled....the tank is solid ballast once the water is in place and is is dampened.......it doesn't roll around, slosh or slam. Like other said, pull back on that throttle if the boat is going to get slammed...heck, I do that on the jet ski, keep my fillings in and my own ballast from taking wear and tear. Like our friend from Bellingham stated, use the boat as designed(well, that may be an issue)but, as she feels capable of doing and be realistic about what she is for, and she'll treat you well......my 96 is still a beauty and I use her!!!!! Randy

[Chip Hindes]

If they feel that just the 8-10 minutes of draining the ballast is a strain on the engine, what is running the boat at full ballast at high speed for long periods doing to the 2 or 4 engine?

What does draining the ballast have to do with it? You can drain the ballast at 1/4 throttle, eight knots, and 2500 motor RPM. You can drain ballast with a 15HP motor, maybe less. If "they" think that puts more strain on the motor than running it WOT, they are, to put it politely, rowing that boat with only one oar in the water.

Running a given motor at WOT, you chose the prop to keep the RPM where the manufacturer tells you it should be. At WOT and the motor manufacturer's specified max RPM, it doesn't matter whether it's a loaded, ballasted Mac with an 11 pitch prop at 13 knots or a 400 lb hydroplane with a 25 pitch prop at 50 knots, the load and "strain" on the motor is exactly the same.

OK, everybody, before you get all carried away, the postulated 25 pitch prop is an exagerration for the sake of the argument.

Running a motor at WOT is harder on the motor than running it slower. It's no different with ballast or without, regardless of boat speed, and no different on the Mac than on any other boat.

[Mark Prouty]

I have been reading the posts on larger engines on the Mac and one of the reasons stated for buying a bigger engine was to plane the boat with full ballast.

I already forked out enough getting my transom fixed when my big motor was improperly installed. I am not going to blast my boat with full ballast through big chop and risk damage to the ballast tank hull joints. I don't feel I stress my boat much beyond its design capacity if I operate it with prudence. Wave and chop have to be negotiated sensibly. I don't like running fast with a full ballast anyway; it is a waste of gas and a wetter ride.

I did feel loss of control once at high speed when I was following another boat. His wake caused me to veer. I'm going to try lowering the centerboard about an inch to see if I can correct this situation; the skeg theory. In addition, I'll be slowing down more under these conditions.

Keep in mind that in these parts, there are plenty of conditions to leverage the big motor advantage. A bigger motor adds another dimension to the powersailer experience. I like to relax on my boat at the end of an awsome day and reminisce about what a good choice my larger motor was.

It's too bad all that raw gnarling power is sitting uptapped under a tarp.


I'm looking forward to towing the younguns on the wake board again and blasting around on a calm day. (I won't be too obnoxious out there. I promise.)

[Dimitri-2000X-Tampa]

Can't say I agree with you on that one Chip. If I run my engine at WOT with no ballast and just me on board, its not just the speed that goes up compared to a full ballast with 6 people on board. Inversely with a heavier load, the carb noise goes way up. To me, this means the intake manifold pressure has dropped considerably and the engine is straining hard to push about a ton more than the designers ever imagined for a 50HP motor. Same deal when flying constant speed propped (variable pitch) airplanes, the power function is one of MP AND RPM.

When I was a kid, my uncle used to pull a bunch of us on waterskis using a 40HP inflatable boat. Never a problem with all of us (under 100lb) kids. Then this girl we knew who was quite overweight and a very good mono skier on her daddy's 175HP speedboat wanted a ride. I watched as the motor strained to pull her (probably around 200lb) mass out of the water before a big pop was heard. Busted that crankshaft right in half. My uncle got a new motor but would only allow 2 ski starts after that.

[Chip Hindes]

Can't say I agree with you on that one Chip.

Perhaps I got carried away in my derision over the ballast emptying statement. In fact, the highest load on the engine occurs not at the max motor speed, but at the max torque speed, which is almost always somewhat lower. Also, at WOT, a substantial increase in load can occur with only minimal decreases in motor speed, as your comment concerning induction noise points out.

The point remains, it has little to do with the speed at which the ballast empties. The question I neglected to ask, though, is why would sombody run max speed with full ballast for more than a few minutes, anyway?

[Moe]

The maximum combustion pressure occurs at the torque peak rpm AND wide-open throttle (WOT). With a properly propped (and geared) motor, one which reaches the manufacturer's recommended rpm range for WOT operation, the maximum combustion pressure is only going to occur momentarily as the boat accelerates through that rpm range. Only a seriously overpropped (and/or overgeared) motor is going to be continuously running at WOT at the torque peak rpm. When able to reach the recommended WOT rpm range with a given load, the motor will have sufficient mechanical advantage over the load to prevent combustion pressure from exceeding the anti-knock rating of the fuel, creating detonation and a much higher pressure load than engine parts were designed for.

At continuous WOT operation, there is some, but little, difference in combustion pressure (manifested as torque) between a heavily loaded (ballasted) boat vs a lightly loaded (unballasted) boat, once again, as long as the rpms are within the manufacturer's recommended range. That's partly due to the increased prop slip with the heavier load, which reduces the difference in rpm. And in both cases, it's less than the pressure that occurs at WOT at the torque peak rpm. There is, however, an increase in piston, rod, bearing, and crank load due to the higher piston speed (compared to that at the torque peak rpm), as the piston is accelerated and decelerated. And wear goes up as well.

Getting back to emptying the ballast tank speeds, you're almost as far on the other side of the torque peak as you are at WOT, so combustion pressure is less than at the torque peak. On 900-1000cc four-strokes that develop peak HP around 5,500-6,000 rpm, that peak is probably right around 4,000 rpm. At MacGregor's recommended speed of 8 mph, you're also only slightly above the hull speed, so the load of climbing the bow wave, much less the load of accelerating while doing that, isn't in the picture, and you should be no where near WOT and the combustion pressure associated with that.

BTW, intake noise doesn't mean the engine is straining. It means the engine is now beginning to put out the power it was designed to produce. And as long as the engine can achieve the recommended WOT rpm range by proper propping, it is NOT pushing a load greater than for which it was designed.

--
Moe

[Divecoz]

I am not an engineer as some are here , however from a practical aspect.
I am associated with a Large Dive Shop on the Island of Cozumel. 8 of the boats being used are in the + or - 30' range all have Large twins on the back and all are now 4 strokes, to save on gas and eliminate fumes but also because they seem to be lasting much longer than the 2 strokes . Problem was and is . . .these are very heavy boats built to handle heavy loads in heavy seas while moving quickly . Most are seldom ever run at WOT. Here in lies the rub btw . Similar boats used only for Sport Fishing and not pushing near the weight seem to last twice as long.
So what does that tell us ? That in fact the stress and strain is greater on a motor pushing more weight . BTW motors in use are Johnson Yamaha Honda and Mercury.. Right now Honda seems to be the best of the bunch but we are waiting to see.

[Dimitri-2000X-Tampa]

I don't think there is enough slippage to be significant as long as the boat is properly propped. If the wear goes up then it figures that it would be straining. And if the crankshaft breaks, I would think that is not what it was designed for.

[Moe]

Trying to pull a fat girl up slalom one time doesn't break an outboard crank. It was either a manufacturing defect, or the last straw in a long history of abuse(s), i.e. overpropping, underpropping, etc.

--
Moe

[Dullboy]

Now Moe, are you saying this engine in an unfriendly environment stays pristine and doesn't have any ill effects under "appropriate" usage?

I didn't think so.


Sorry Moe, I'll let you answer for yourself.

[Moe]

I have no idea what your question is, or what you mean by "unfriendly environment" or "appropriate usage"

--
Moe