MacGregorSailors.com

50hp

Ok, have we wandered off the OP thread? Asa I recall, the OP was looking for the largest outboard that could be pull-started if needed.

Sheppie62 wrote: ↑Thu Jan 13, 2022 6:52 am The Yamaha 70 AND Suzuki 90 seem to be most common options. But I have no experience with or experience with these motors. Anybody want to add info to this? What does blue water yachts recommend now? I don’t think you could aggressively single ski with a 90, I’m thinking it would slow the boat down when skier turns. Maybe casual skiing? Realistic speed with normal load?

PopeyePete wrote: ↑Sun Sep 01, 2019 2:06 pm 1)What is the maximum horsepower I can put on a 2001 26 x?
2) What engine would be the best to achieve it?
3)What speed (with and without water ballast) can I expect to get?
4) would it have enough power to pull up a slalom skier?

From the original thread.

You know, that after the initial posting, PopeyPete never entered the thread again.

I just sent an e-mail asking what Pete's final decision was; inquiring minds want to know.

OverEasy wrote: ↑Tue Jan 11, 2022 9:30 pm
Hanging increasingly more powerful and heavier engines on a transom and hull designed for 50 hp progressively “eats into the design margin”. .

..The increase in additional stress is roughly a square function increase with additional power.

What is the exact numerical safety factor in Rodger's design margin? Based on what?

The stress does not increase by the square of additional power (F=MA). Drag does go up by the square of the velocity but would be more of a reducing function curve when on-plane.

Before we installed our no problem 90 we looked a Suzuki dealership center console boat which had a no thicker transom than the Mac with a 150 hp installed.

Need real engineering data to prove there is an issue, not guesses and opinions.

Please provide.

Thanks,

Victor

Personally we made the decision to go to a 90 after I felt there was enough "experience" to challenge the design calculations. If no one else had done it, I wouldn't have been the pioneer, but so many had already done it with positive outcomes, including the 140 on Billy's and the 115 on Greg's that I felt comfortable with the risk.

For me, tribal knowledge tops deference to Roger's design process.

That said, the first time a 26X has a structural failure due to a 90HP I'll sell the motor the next day. I just hope it isn't mine that pioneers the failure mode.

Interesting article which attempts to shed some light on outboard hp vs transom load, taking into consideration various degrees of motor setback. Unfortunately, the article starts at 125 hp and goes up. But the trends are interesting. The transom stress vs motor hp is a fairly complex analysis that really can't be captured easily in general discussions. Note these numbers are for a 20" shaft.

I'd be very interested to see Roger's calculations on the transom design for the X or M. In fact, I'd be very interested to know if there were any.

I haven't verified any of the numbers in this article. So, read with a critical eye.
https://www.rrrtoolsolutions.com/stress ... som-stress

Starscream wrote: ↑Mon Jan 17, 2022 4:58 pm That said, the first time a 26X has a structural failure due to a 90HP I'll sell the motor the next day. I just hope it isn't mine that pioneers the failure mode.

Hi VkMaynard

That is the point!
There is no publicly available design data or calculations issued for the Mac26X or Mac26M.

The manufacturer made a max engine size determination and recommendation. Just tossing on larger engines without consideration of the implications isn’t something any reputable qualified design engineer would do.

Just because someone “gets away” with something beyond the manufacturer’s recommendation doesn’t make it valid.

Typically a minimum competent responsible commercial consumer engineered design margin is 25% or more above recommendation before failure.

The above is a baseline point consideration.
Designing in additional margin costs money, materials and time all of which increase product cost. Not something a manufacturer does lightly.

Rodger MacGregor was and is a competent designer and he had competent design engineering staff. They deliberately made the decision to limit the recommended horsepower to 50 hp for the Mac26X and 60 hp for the Mac26M.
They deliberately chose to limit their market window. It’s important to bear that in mind.

Transom thickness is only one aspect. Corner structure for load transfer to the forward structure is another. Hull thickness and internal supporting structure are among several others that have to be accounted for. Then there are also the loads imparted during land transit. A good pothole or two at speed can generate substantial stresses. Repeating impacting stresses (such as generated on poorly maintained concrete highways) are another consideration that affects not just the transom but also the hull and supporting structure.

Wave / hull / speed loading interactions are challenging design consideration aspects. The faster a vessel attempts to move through the water the higher the hull stresses. Wave pounding depends upon wave frequency and height and speed. The hull in the Mac26X is relatively thin as begets a trailerable motorsailer. Higher horse power allows for higher speeds which can increase hull stresses. This is why powerboats designed for higher speeds have substantially thicker hulls and more robust stiffening structures.

So if someone chooses to hang an engine substantially greater than the manufacture recommended they are doing so “at risk” and the engineering term for that is ‘pioneering’. They don’t have any design data to support their decision. They basically choose to do it because they want to and “hope to get away” with it.

It’s their boat and their choice to be “pioneers”.
The hope is that prudence in operation is used and they slow down in other than smooth calm conditions. Water is unforgiving to people and boats. When things go sideways there can be real consequences.

I’m glad that there haven’t been catastrophic failures or damages. That’s a good thing as no sane person wants anyone hurt.

But there is no definitive engineering basis to substantiate substantial horsepower increases above the manufacturer’s recommendations.

Your free to do with your boat as you see fit but realistically you are also responsible for those choices.

Best Regards
Over Easy

Hi JimmyT!

Nice article!
The author’s focus is on heavier hulled and structured bass boats but did a good job of presenting good considerations and maintenance practices (like properly torquing bolts and repeat checking over time).

Best Regards
Over Easy

OverEasy wrote: ↑Mon Jan 17, 2022 9:21 pm Hi JimmyT!

Nice article!
The author’s focus is on heavier hulled and structured bass boats but did a good job of presenting good considerations and maintenance practices (like properly torquing bolts and repeat checking over time).

Best Regards
Over Easy

Motor thrust, and transom load trends, as a function of motor hp, were what I found interesting in the article. The impact of motor setback was also enlightening. These numbers are independent of transom/hull design (other than the impact of long shaft vs short shaft which is potentially a function of transom height/motor well design - if not using a transom mounting bracket of some sort).

in general, the article gives insight to how transom loads increase with motor hp for a given setup. This seemed to be part of the discussion earlier. Just thought I would throw it into the mix...

OverEasy wrote: ↑Mon Jan 17, 2022 8:59 pm Hi VkMaynard

That is the point!
There is no publicly available design data or calculations issued for the Mac26X or Mac26M.

The manufacturer made a max engine size determination and recommendation. Just tossing on larger engines without consideration of the implications isn’t something any reputable qualified design engineer would do.

Just because someone “gets away” with something beyond the manufacturer’s recommendation doesn’t make it valid.

Typically a minimum competent responsible commercial consumer engineered design margin is 25% or more above recommendation before failure.

The above is a baseline point consideration.
Designing in additional margin costs money, materials and time all of which increase product cost. Not something a manufacturer does lightly.

Rodger MacGregor was and is a competent designer and he had competent design engineering staff. They deliberately made the decision to limit the recommended horsepower to 50 hp for the Mac26X and 60 hp for the Mac26M.
They deliberately chose to limit their market window. It’s important to bear that in mind.

Transom thickness is only one aspect. Corner structure for load transfer to the forward structure is another. Hull thickness and internal supporting structure are among several others that have to be accounted for. Then there are also the loads imparted during land transit. A good pothole or two at speed can generate substantial stresses. Repeating impacting stresses (such as generated on poorly maintained concrete highways) are another consideration that affects not just the transom but also the hull and supporting structure.

Wave / hull / speed loading interactions are challenging design consideration aspects. The faster a vessel attempts to move through the water the higher the hull stresses. Wave pounding depends upon wave frequency and height and speed. The hull in the Mac26X is relatively thin as begets a trailerable motorsailer. Higher horse power allows for higher speeds which can increase hull stresses. This is why powerboats designed for higher speeds have substantially thicker hulls and more robust stiffening structures.

So if someone chooses to hang an engine substantially greater than the manufacture recommended they are doing so “at risk” and the engineering term for that is ‘pioneering’. They don’t have any design data to support their decision. They basically choose to do it because they want to and “hope to get away” with it.

It’s their boat and their choice to be “pioneers”.
The hope is that prudence in operation is used and they slow down in other than smooth calm conditions. Water is unforgiving to people and boats. When things go sideways there can be real consequences.

I’m glad that there haven’t been catastrophic failures or damages. That’s a good thing as no sane person wants anyone hurt.

But there is no definitive engineering basis to substantiate substantial horsepower increases above the manufacturer’s recommendations.

Your free to do with your boat as you see fit but realistically you are also responsible for those choices.

Best Regards
Over Easy

This is a solid argument for staying with the manufacturer's recommendations. I totally respect this position.

There are a few counter-arguments that I had to consider in making my choice. The first was, as I said, the number of X's that had 90's successfully installed. When I made that decision there were dozens that I knew of, running for long periods of time, including that 140HP 26X. I counted that as valid R&D test data that Roger's team never had. If the 90HP data was anecdotal, or some guy that I heard of, I wouldn't have done it.

Another counter-argument that I considered was the risk-averse level of the manufacturer. A boat manufactured in the USA and exposed to the US legal system must be extremely overdesigned to protect the manufacturer. That fact is evident in all the Macgregor warnings all over the boat and in the manual with regards to crew position, weight, HP, loading, etc. My experience over several years of operating it with a 50HP is that it was waaay more stable and safe than the manual and stickers made it out to be. Over the years I've experimented with the boat to establish my comfort level: I've sailed at 45 degrees in heavy winds in an attempt to get knocked down (couldn't do it), I've motored with a 90HP through huge wakes with people on the cabin-top, I've sailed without ballast and with partial ballast, I've done full throttle hole-shots with the motor hard over (very fun, actually), I've powered up to full power with the centerboard down both ballasted and unballasted, I've overloaded the boat with 8 people, I sail regularly with 5 people and gear that puts the motor-well drain below the waterline, and probably a few etc.

I'm not recommending any of this, of course. I did most of it with informed friends with safety gear in friendly waters, but I also did some of it by accident.

The boat is waaay safer than most people think. This idea is borne out by the sheer number of boats produced: with over 15k X's and M's out there, statistics say that many (if not most) are in the hands of...umm how do I say this...people who don't understand....much...of anything. And despite the tragedy on Lake Champlain I believe that the safety record of the Macs is unparalleled. Which means to me, overdesigned.

With regards to MacGregor's R&D, I'm willing to bet that there wasn't much actual R&D done. Without any knowledge of the actual process of the X, I'm willing to bet that the base R&D went along the lines of going out and measuring the transom of some boat rated for something like 70HP and then making the X transom thicker/stronger than that. Which is a valid R&D method, in some cases, but risky when dealing with boats, so I bet that they made it waaaay thicker/stronger than that.

Anyway, to each his own. I know that along with my decisions comes responsibility. I've decided that for me and my family, the 90HP is a low-risk decision.

I do enjoy these conversations. Different opinions are the spice of life (unless they are political or religious, then get out, as fast as you can!)

Found this in the "how it all started" narrative.

Roger's masters degree is in business administration. Don't know about his undergrad. Anybody know?

At any rate, he doesn't claim the "complex structural calculations". Those were apparently done by naval architects...

Neither here nor there. Just keeping it real.

DESIGN PROCESS

All of our design work was done within the company. We did rely on naval architects to help us with complex structural calculations. I’ve attached a drawing of our rather powerful computers and a giant 41" screen that enable us to create digital images of every single part on the boat. These computer images were sent to computer control milling machines that provided all of the cross-sections we needed to create the plugs. (Plugs were wooden and fiberglass mockups over which the fiberglass molds were laid.)

Computer design enabled us to hold remarkably tight tolerances, and easily experiment with alternative design ideas.

OverEasy wrote: ↑Mon Jan 17, 2022 8:59 pm Hi VkMaynard

The manufacturer made a max engine size determination and recommendation. Just tossing on larger engines without consideration of the implications isn’t something any reputable qualified design engineer would do.

Over Easy

Based on what? Cost, more compact size, pull start?

So Blue Water Yachts is in violation installing 60 and 70 hp motors on these boats? Exactly how much did they reduce the safety margin?

Again please provide real data instead of guesses and fearmongering.

We have about 300-400 hours runtime on our 90 since 2010 with no issues. That includes wake boarding initial pull stress.

Thanks,

Victor

Thank you all for this discussion.

I’m learning so much from reading your points of view. As most things, it comes down to your risk tolerance, risk awareness and risk mitigation. By you discussing your points, I’m getting a better understanding of the overall risks with a powerboat and the specific risks of powering a Mac. Thanks!!