Powering with full ballast

[BK]

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. It is stated in the manual that each 100LBs of weight in the boat reduces speed by one MPH. At 1400LBs of water in the ballast, a lot of power will be needed to move the boat at high speed. Also, I think the boat was never designed to carry a full ballast at high speed and could be a safety issue. I would check with Macgregor on this point as that is a lot of stress on the F/G. As far as I know we have never discussed this before and did not want it to get lost in 60 replies. Alot of money for something the boat was not designed to do.

[Dimitri-2000X-Tampa]

My boat planes with full ballast and a 50HP..even with 3 adults and 4 kids on board. It may be straining, but its still planing.... (for Mark)

[mark,97x]

because of the orders from the mate,my ballast tanks are always full,i really dont know how much of a plane i get on but we usualy power at 13-14 mph(50 hp) and have not noticed any damage to the in fact she seems to be holding up thru the years better than the mate

[Duane Dunn, Allegro]

OK, let's not debate planing again. Let's use the term going 'faster than hull speed'.

I think you are perfectly fine powering the boat with the ballast tank full at 'faster than hull speed' speeds up to what the 50hp is capable of which is around 12 knots (13.8mph). Going faster than that with the big motors is what MacGregor has offficially stated can cause damage. They are not concerned for the hull itself, but are concerned that the ballast tank to hull joints will separate if you pound the boat at higher speeds with the tank full.

You really just have to be prudent in how you choose to use the extra power on the back. Without a doubt, if you use it carelessly there are many ways to hurt the boat.

Just as an aside, for many years we have operated our boat with the tank empty at all speeds in all conditions with my family aboard without even hint of any bad or threatening behavior from the boat. If we are going to be motoring for more that 10 minutes somewhere we always empty the tank. Why waste the gas and sacrifice the speed? The boat is perfectly safe and comfortable powering with the tank empty.

[Billy]

FWIW, I have powered full ballasted and loaded at 25 mph with no problems. The water had a slight chop and the extra weight seemed to give the boat a smoother ride. (About 3 mpg, but if you buy a big horse, you have to feed it.) These boats are lightweight, but they are not fragile (barring abuse).

[Chip Hindes]

I would check with Macgregor on this point

Waste of time. The idea that Mac is going to contribute anything, even an offhand comment, that might encourage somebody to exceed their recommendatin on max HP seems like it must be somebody's fantasy. Their answer will be, as it always is, "Read my lips: 50 HP max. End of discussion."

Which briings up the next point:

They are not concerned for the hull itself, but are concerned that the ballast tank to hull joints will separate if you pound the boat at higher speeds with the tank full.

Interesting claim, and if true would seem to indicate all those who are repowering at higher HP are wasting their time with the transom reinforcements, while doing nothing about the ballast tank to hull joints.

Do you have an actual quote or statement on which to base this claim? If so, did it come from the designer, the warranty department, or the third rest room cubicle on the left, so to speak?

[Frank C]

Yes. When I insisted on a Suzi60 (or wouldn't buy the boat) my dealer apprached the factory about extending the hull warranty. I am just guessing that nobody else had ever asked in August 1999, and the 1300cc Suzuki was a big step larger than the 900cc Merc Bigfoot.

However, the factory described their belief that the transom would handle the power and weight of my outboard (at 335#), since they had previously invested some time and effort testing the integrity of the transom. He said they spent a weekend (maybe with one of the prototypes) trying to "tow a dock" at full power.

However, they specifically declined to warrant the hull against the potential abuse at high speeds. Gene Arena, my Mac dealer, said the ballast tank, especially when full in heavy pounding, was an untested risk. If one simply imagines the "design process" at a small company, creating the first motorsailer in the market, it's no stretch to guess that they WOULD test the transom pretty well. After all, they were building their first full transom-mounted heavy motor .... coming from the Mac 26 classic sailboat, plus a short-term experiment with the Mac 19. It seems quite logical that Roger WOULD INDEED test the transom on this new design, don'cha think?

[Chip Hindes]

It seems quite logical that Roger WOULD INDEED test the transom on this new design, don'cha think?

Yes, but that's irrelevant, because the use of logic in this situation is not warranted. By the same logic I would have to assume they tested the hull to tank joint as well.

If an test engineer that worked for me told me his entire test of the ability of a boat to handle a new, bigger motor consisted of trying to tow a dock at full power, I'd have to consider firing him for incompetence. If I'm imagining the design process at Mac as you suggerst, not in the furthest stretch would I come up with, "Tow a dock, but don't test the hull to ballast tank joint" as the basis of my test regime.

It reminds me a lot of drilling a hole in the bottom of the boat as a demonstration of stability and unsinkability. Interesting, photogenic, great for a marketing blurb, makes a really great story for the unitiated, somewhat better than nothing, but ultimatley, not worth much in a real world application.

I'm not doubting that you're quoting accurately what you heard from your dealer quite a few years ago, but it's not even close to what would qualify in my book as real, useful information from the designer. Or test department, for that matter. It's way closer to what I was describing: third rest room stall on the left.

We have quite a few anecdotal examples of larger motors now, and to my knowledge nobody has yet reported hull to tank failures or cracks. We do have one transom failure (was it Mark?) but I belive there was some question that the reinforcements poorly executed may have actually caused the failure, not just failed to prevent it.

[Duane Dunn, Allegro]

Everyone gives Roger far to much credit as a boat designer. He is NOT a naval architect, he is an MBA. MacGregors design cycle consists of a scribble on a napkin, build it, try it, if it didn't break sell it, then try to squeeze out more costs by repeating. Everything at the company is driven by economics, period. These boats are not being professionally designed and then run through a battery of fatigue tests. It's just not how the company works. All that costs money and that is one thing MacGregor has a rock solid history of not spending.

Operate the boat intelligently and it probably won't break. Billy is not out jumping waves a 25 knots with the tank full. From everything I have heard he uses common sense so as one would expect, he has had no problems with the bigger motor.

My explanation about the concern I wrote above comes from dealers who have very close relationships with Roger and the factory. They state that the factory feels the most likely failure if you abuse the boat with the tank full will be the ballast tank to hull joint. That doesn't mean you shouldn't get the big motor if you want it, it's just another data point to keep in mind when you make decisions at the helm.

[waternwaves]

Anecdotes aside.....

This thread seems interesting, so I will give a full report when done with my inspection.

Have any of you actually taken the time to take a borescope or flexible camera and actually gone into the bilge to look at these joints... used a thickness gauge or measured the thickness of the hull adjacent to the tank mounts.. Measured the thickness the tanks..., calculated the moments of inertia of a damped (tanked) fluid.

Note to the wise...
Macgregor hulls flex. noticeably (anyone who has opened a bilge and stuck their hand on the hull in the vicinity of where the waves impact the hull during rough water operation can attest to this....nothing new here)

The acceleration/deceleration of the hull falling/rising in waves and impacting a ballast tank support, (or any 'tank' for that matter) are relatively low.... compared to impact forces with terra firma.


This is another problem that just may be mislabled....

just when I thought I was going to have day when I would not be going under the boat or into the bilge....


For a further enlightening detail.. please look again very carefully at the Mcagregor 26X brochure pic which has most of the component parts of the macgegor laid out adjacant. I am measuring my own to see how close this comes to the construction of mine

Then go look at your own hull by lifting the bilge acces covers.... tell me if anyone sees any non continuously glassed boundaries of the ballast tank.

Then I will let you know the results of my inspection....

Remembering of course that the most of the weight of the water is continuously supported by the bottom of the hull...


Keep looking, I need to look again at the very forward part of the ballast tank......to finish the inspection.....

I think I'll take some pics of this one.

but what the hey, Dont let the real boundary conditions and actual installation details, as well as the laws of newtonian physics, fluid dynamics and actual inspections lead us anywhere.....lol..

Lets see....comparing forces here

70 hp motor, 18" above the reinforced edge of the waterplane... (pushing on a fiberglass plate less than 1/2 inch is supposedly less likely to fail than tank integral to the waterplane, glassed bound volume, located in the part of the boat that also reinforced/stiffened by the centerboard trunk.... and other tank sides...

Moe.... I get to draw the diagram this time lol.......

[BK]

I remember going over some waves caused by the big power boats and ferries in the Puget Sound which the boat shuttered or vibrated badly. You almost have to come to a full stop sometimes if you are too close to their boat. There is no way to to get around this problem unless you own the the whole lake and it is smooth as glass everyday. The stress of waves pounding the boat with a full water ballast at fast speed surely would cause a problem with the F/G. F/G is not steel. Imagine all that water being lifted up in the tank when it hits a wave then slamed down into the bottom of the tank. That is what is happening. Water is a liquid and it moves. I think you are pushing the limit going over 6MPH with a full ballast while sailing. This water ballast has to be the weak link in the design of the Powersailer. I would bet money that Roger would say no to the water being in the ballast at high speed.

[waternwaves]

Please, contents of my note were a comparison of stresses on structures of the boat.

I did not say that pounding waves do not stress the boat.

What I said was that particular joint/mount/location as people call it (between the hull and the ballast tank) is not stressed as high as the top of the transom, when pounding through the waves. And I dont know about your boat, but when the waves are 6 ft, I am not going fast enough to lift any part of the boat out of the water due to planing from the engine, only surfing down the waves.

At at that time only the forward part of the bow( front 7 or 8ft.) of boat is unsupported, and catches the impact strike of the next wave.
Wheras the transom is being flexed by the motor thrust and climbing some of those waves takes considerable thrust which is all applied throught the transom , Other locations getting considerable stress in those kinds of seas include chainplates, mast step.

Hope this clarifies my position, I do not condone trying to power through 5 ft seas at 22 mph in a Mac, nor do I find that ride comfortable in a Marlin, or a Bayliner (well, mabye a 4788) or a grady white. It is hard to get a comfortable ride in moderate seas, or in any short boat in Seas 5 ft +, at 20 + mph.


So yes, rough seas cause problems to fiberglass, but those structures that fail firs, mac included are located around the engine. Since most of our boats live on trailer has anyone found signs of gelcoat crazing, or crackg on the bottom of the hull from forward of the centerboard back to the last 6 or so feet of the boat., or inside between the ballast tank and the hull, now compare that to the flexural cracking and crazing of gelcoat or skin cracking around the transom.


And as far as saying no to full ballast tank at high speed, you have to be above 8 kts, it seems just to drain the tank the way most boats are loaded. Are you saying the Roger designed a boat that should never have the tank drained by the application of speed from engine power???

I have many warning labels on my boat......that one is not there. YOu have to go faster than 6 mph to drain it, and many prefer the stability the ballast offers in heavier seas. (I for one).

Now for the discussion of "fast speed" with full ballast. I am lucky to get 12 mph with a full ballast tank. and the bow does not lift any more than any other macgregor, and there are no 90 degree angles on the waves. no sharp edges, except on the transom...

Having crossed many large wakes (including washington state ferries and the rest of the tanker/container/naval/pleasure vessels) in all of my boats under 30 ft., angling into the wake is always more comfortable.

water in the tank accelerates downward at approximately = to gravity (Except for minor differences due to how far any point is from the center of the boat due to pitch changes, and any lift or drive from the motor, or force from the wind.) There is no slamming as you call it in comparison to dropping a bucket of water on pavement, 100's of G's of decceleration on the bucket surfaces.

My comment was to have people look at how the ballast is supported directly on the inside of the hull.
and was a comparison of forces on the structure of the boat, the transom is joints have higher forces applied perpendicular to the skin of the boat over a smaller area. normal load There is approximately 40- 50 lbs per square ft of hull due to water pressure , and several hundred lbs of pressure from the outboard spread out over less than a square foot of transom., While we cannot directly compare apples and oranges here, at speed, THe middle of the hulls have a enough tensile and shear strength and are not likely to pull apart at this location.

[BK]

Newtonian physics and fluid dynamics; what goes up in the tank must come down. The only thing is what degree and that is my point. At one MPH the movement of water in the tank when slammed by a wave is small. At 25 MPH with a full ballast the degree of water movement in the tank when slammed by a wave is dangerous.

[waternwaves]

Whoaa.
lets get back to reality here.....
1) who has a mac that can do 25 mph with a full ballast tank (thre might be one in here) An no one is recommending 25 mph in heavy seas.
2) Suposedly the tank it full, That is what the little tiny vent that we are supposed to open is for, to determine when the tank is full. in this boat we are told tank is empty or full, or being filled or being drained, those are the approved modes of operation, partial tank is not a regular cruising mode. it is a transition of a few minutes between modes.
3) A filled tanked is a Semi damped system and analyzable. a wall of water striking a wall of water does not result in tremendous displacement, The boat flexes and slides past , and the hull provides for that flex over a very large area, that is why there are no cracks in that location.

So functionally there is no "water movement" in the tank when full.

Sections of the boat slip deeper into the water and rise back

I understand your point, and I dont recommend jet skiing with a mac at 25 mph over 6 ft waves., but it doesnt matter if the weight is ballast, passengers, microwaves, bunks, cabin furniture etc.... how those weights are attached to the hull indicates sufficient and significant area for those loads. That is why we dont have cracking in those areas, It sounds bad because the boat is an acoustic drum, and sitting in the cockpit with the hatch open (Something I dont recommend in 6 ft. seas,) allows the operator to hear a hellacious amount of noise from the macgregor drum.


The forces on an unreinforced transom, trying to power a regularly loaded mac through those kind of speeds and seas..... would result in overstressing the transom first. And the amount of horsepower to get the boat to make those speeds.... (I am guessing here, but the 140 is probably required) is significant.

So thus without empircal evidence ( any macgregor of the 5,000 ) with hull cracking in that location, nor the rough examination of forces.., nor with any reported delamination between hull and tank, and with fairly complete inspection of two boats,(covers off, lights in, rollers to flex, nor the purchase inspections of 17 boats, Of which 10 had no bottom paint and were thus available to inspect more closely, none of those boats had any sign of flexural strain or cracking .

However, of the 50 hp powered boats I looked at, (14 of the 17) 5 had minor cracking, craizing and stress indicatons around the motor mounts/transom. (including the trim strip in the walk through area of teh transom). So, from this I gather that that the area that can use the most reinforcement is the transom.

In regards to your original thread topic,

1) it woud be interesting to see if anyone thought that carrying full ballast at over 15 mph is even necessary, Seems to me sea state puts a considerable crimp on ride comfort long before the waves reach 6 ft. and though I have done full throttle/full load, heavy seas operation to get out of particularly nasty situation, normally I suspsect most of us have reduced speed to 10 -12 when the pitching is that intense.
2) the "lot of power" you describe to move the boat that fast is applying all that force in a considerably smaller area than across the front of the hull.

Thanks for the opportunity to clarify my statements.

[BK]

Its been awhile since someone has mentioned this but you can superfill your ballast tank by backing up the boat with the ballast open. If the tank can take more water than just normal amounts by doing superfill then that means there is excess space in the tank for the water to move around.