Re-powering a MacM from 70 HP up

[beene]

Highlander when you allegedaly plane your boat , is the cavitation plate at the water line , or there abouts ?

Here you go

http://s166.photobucket.com/albums/u119 ... 010033.mp4

G

[Highlander]

Well Geoff & I were talking to a Mercury Rep. at the boat show about the opti-max 150HP Two Stroke it weighs about the same as my 75HP F/S so we were thinking twice the horse power HMMM!

But suprise suprise he told us for our boats better off to stick with the Four Strokes twice the Torq Range ! & thats what yer want to get the boat up outa the water !! Lots of Torq


J

[Highlander]

And now to Kick Beene's Butt
http://i844.photobucket.com/albums/ab1/ ... 010011.jpg

http://i844.photobucket.com/albums/ab1/ ... 010012.jpg

Come on spring

J

[Gypsy]

Highlander when you allegedaly plane your boat , is the cavitation plate at the water line , or there abouts ?

Here you go

http://s166.photobucket.com/albums/u119 ... 010033.mp4

G

When my Bayliner was on full plane the cavitation plate was riding on the surface , it was visible.
It might have been the video , but I didn't see a cavitation plate.

There is no doubt you are going very fast , probably going the speed of a planning boat . But I don't think it is actually planning , just moving thru the water , very ,very , fast !

[Octaman]

Highlander,

Will be very interesting to see what you get out of the 13 1/4 (diameter) x 17 (pitch) on your Merc.
I thought a lot about what the starting point should be on my new Suzuki 100 - expected to arrive very soon.
Decided to startwith 14 x 17. Should be about right.

Octaman

[waternwaves]

cav plate depends on motor model, setup and length of leg,

doesnt change how the boat hull is riding.

planing refers to the hull.

[ROAD Soldier]

Highlander,

Will be very interesting to see what you get out of the 13 1/4 (diameter) x 17 (pitch) on your Merc.
I thought a lot about what the starting point should be on my new Suzuki 100 - expected to arrive very soon.
Decided to startwith 14 x 17. Should be about right.

Octaman

According to the Suzuki website the 100 is the same weight as the 140 so why didn't you get that one You Chicken

[Highlander]

Highlander,

Will be very interesting to see what you get out of the 13 1/4 (diameter) x 17 (pitch) on your Merc.
I thought a lot about what the starting point should be on my new Suzuki 100 - expected to arrive very soon.
Decided to startwith 14 x 17. Should be about right.

Octaman

According to the Suzuki website the 100 is the same weight as the 140 so why didn't you get that one You Chicken

Their yer go again more HP don't mean ShiI without Torq Baby , so whats the torq range

J

[ROAD Soldier]

Ok now you made go and do it. Because of the manufactures BS and the BS being passed along here I had to dig out my old motor-head formulas that I used back when I used to spend thousands of dollars to shave off a few seconds in a quarter mile.
Horsepower * 5252/RPM=Torque
So looking at the little bit of information the manufacture Suzuki gives us which is operating RPMs only not when maximum HP produced (which is what we really need) the numbers are as follows:
140HP O/B 5600-6200 RPMs
100HP O/B 5000-6000 RPMs
Now since maximum HP is "usually" produced before maximum RPMs let's assume that maximum HP for the 140 is at 5600 RPMs and the 100 is at 5000 RPMs since this basically tells us that you should not put a propeller on that will not allow the engine to reach at least those respective RPMs in order to operate at maximum HP. We can figure the follow torques:
140HP O/B=131.3 lbs of torque at 5600 RPMs
100HP O/B=105.04 lbs of torque at 5000 RPMs
Now since both engines weight and gearing is exactly the same we can further figure that 100 is 71.43% of 140 that at 5000 RPMs the 140HP engine would produce 93.79 lbs of torque. So the 100HP engine has slightly more low-end torque. Now how fast the 140HP goes from 5000-5600 RPMs is going to tell you how much if any the slight difference of each engine takes to get to 5000 RPMs. Torque is a measure of how easy the engine moves, the more torque the faster it will reach a certain RPM. So the 100HP will reach 5000 RPM before the 140HP but only slightly and it will never reach 5600 RPM assuming both engines are maxed out on propeller pitch for the same weighted and model boat. Great now my head hurts.

[beene]

Thing is..........
I was sold on the Merc 150 Optimax
thing weighs about the same as my 75
but it is a V6 vs inline 4
and over 1000 cc more omph
so i was sold on the idea

we spoke with the rep
he talked me out of upgrading

he said the 150 has more torque and more hp, but up top, not down low in the rpm band

????

he said that what will work best for our boats, basically a waterbeggoes, is the 75 4s with the fuel injection
why????

because you get all the torque right away
when you need it

the 150 is designed for a bass boat
it will just keep climbing and climbing.......
faster and faster............
40 50 60+ mph

whereas with our boats
we dont get those speeds
we just want our boats to get on plane and stay there with no fuss about it
load the thing to the gunwales and still rock on

it would seem the 75 and 90 models out there are doing a great job of just that

i for 1 am very pleased with the performance i get from my 75
the 1600cc big block kick the boat out of the hole with ease
back off the ttl and sit on plane at 3/4 ttl
smooth and quiet

.02

G

[Highlander]

Highlander,

Will be very interesting to see what you get out of the 13 1/4 (diameter) x 17 (pitch) on your Merc.
I thought a lot about what the starting point should be on my new Suzuki 100 - expected to arrive very soon.
Decided to startwith 14 x 17. Should be about right.

Octaman

According to the Suzuki website the 100 is the same weight as the 140 so why didn't you get that one You Chicken

Well I just went into the Merc site & clicked on their Prop Calulator , put in all my info & low & behold it tells me my best prop should be the 13 / 1/4" x 17 so I am a happy camper right now anyway until trial time but when I was talking to the prop guy @ the show he told me the same thing ! so I guess he did know what he was talking about ! ? "I hope"

Oh by the way I see the Merc 90HP 4/S now has the same torq range as the 75HP 4/S ! very interesting so yes if I was to do it again today knowing the new torq ranges I'd go with the 90HP !

The 75/90HP eng's have a WOT range of 5000/6000RPM's thats a 1000RPM Torq range & the 115HP eng's have a WOT range of 5800/6400RPM'S thats a 600RPM Torq range

So the two smaller HP eng's almost have twice the torq range of the bigger HP eng. !! ?

Now if you really want to see an Eye Opener go & check out the boat test's done on these eng's by the boat manufactures you'll see that the bigger eng. with less torq will run slightly faster 2-3MP/H. BUT your fuel consumption will double or more because the bigger eng. with less torq is working its darn butt of trying to reach it's torq range before it starts kicking Butt

Now take this into consideration your Mac is not a Deep V-Hull so you are not able to run at WOT in 12-15ft sea's . no when you run at WOT the water is like Glass - say 4ft sea's Yep here's the proof
http://s844.photobucket.com/albums/ab1/ ... 010052.mp4
I know he is slightly demented !

The higher torq eng's seem to have a better fuel rate @ WOT & at the 1000RPM's & 4000RPM'S range & thats where your Mac comes in 1000RPM'S for power sailing & 4000RPM'S for Cruising

Yep We are not running the 1/4 Mile track

J

[Gypsy]

cav plate depends on motor model, setup and length of leg,

doesnt change how the boat hull is riding.

planing refers to the hull.

This is True !
But on a planning boat , the cavitation plate should be level with the bottom of the hull .
A long legged sailboat outboard , would have the cavitation plate well below the bottom of the hull , and not be good for planning. Where as a short legged racing outboard , wouldn't do anything on a Mac , but churn up water.

By the fact that I own a planning cabin cruiser , I was looking for comparisions , to try and determine whether Highlander is truly planning or not.

There is no doubt He is going planning (Or faster)speeds , but whether He is truly planning is the debate ,
and in my humble opinion , He is not.

[Catigale]

The 75/90HP eng's have a WOT range of 5000/6000RPM's thats a 1000RPM Torq range & the 115HP eng's have a WOT range of 5800/6400RPM'S thats a 600RPM Torq range

So the two smaller HP eng's almost have twice the torq range of the bigger HP eng. !! ?

Im not sure what this means. The WOT range is given to guide prop selection - I dont think you get guaranteed torque or HP ratings from manufacturers over this range. Usually you only get HP specified at a single rpm.

[ROAD Soldier]

Yep We are not running the 1/4 Mile track

J

You’re not running your boat in a ¼ Mile here, what is wrong with you? Did you know how much information you can get from a ¼ Mile time? If you were really anal you could figure out the exact (real world) torque, HP, and power-band that would take into account wind speed and coefficient drag of your boat. Hence the term real world which you will find is different and more accurate than a dyno-machine. Unless your engine is sitting still the dyno-machine is not 100% accurate. If you really wanted to be anal you could put your boat and yourself on a scale subtracting the weight of the trailer then measure a 1/4mile on the water marking it with buoys and then use a stopwatch, video camera aimed at your RPM gauge and your stopwatch at the same time, and a whole lot of math you could figure out your HP, Torque, and power-band at any given RPM. Now you can eliminate a lot of the math and work by using one of these http://www.driftbox.com/performance_meter.html. I have an older one that doesn’t use GPS and has to stay level, and measure a level surface which simple would not work on the water. Water doesn’t stay still like a road. Now using the stop watch method is easier to do it with 2 people and requires a whole day or several days work sometimes because you also want the same air temperature and humidity each time to. Using the driftbox would be half a day because if you wanted to be an anal exact person like I used to be you still need to weigh your boat, self, and buddy. To give a complete step by step instructions on using the former method I would have to write a small chapter here. I am not going to do that. Now another easier method of figuring out the best most efficient engine or even the best propeller for the engine you have is simple run a run your boat from zero to WOT in a quarter mile and whatever is the fastest time is the best most efficient motor/propeller for your boat. Quarter mile is a good length because it throws out nonpower-band torque, say an engine that goes from 4500RPMs to 5500RPMs in days from now.
Now let’s talk definitions first one is operating RPMs. Operating RPMs on a car is simple where the engine stays running which is from idle to redline. This is definitely not the definition that Marine Outboard Manufactures use unless your engine idles at 5000 RPMs or there about. Which would make things real interesting at the Marina when you shifted into forward or reverse.
So here is where I maybe wrong, only because I just cannot confirm exactly what the Marine industry doesn’t tell you like the Auto or Aviation industry does. I believe using my mechanical logic as a mechanic that Marine Operating RPMs is where the engine generates the most HP and Torque for a given propeller. So if you’re operating RPMs is say 5000 to 6000 then if you use a larger diameter/pitch propeller that still allows the engine to run at 5000 RPMs then you would get about the same speed with a smaller diameter/pitch propeller that allows the engine to run at 6000 RPMs not counting any difference in internal friction of the engine. So that 600RPM spread versus the 1000RPM spread is simple the range you are allowed to play with to choose the most efficient propeller for you boat design. The best propeller within that range would be proven by doing what? The quarter mile time because it would give you the best torque curve or power-band from idle to the Marine operating RPM, the faster your time the more of a power-band you have a lower RPMs. That 600 or 1000 RPM range is not a torque curve. The torque curve is before it and the part before it the raises the quickest like say 2000 RPMs to 4500 RPMs would be the Power-Band.

[Octaman]

RoadSoldier

According to the Suzuki website the 100 is the same weight as the 140 so why didn't you get that one

The 100HP and 115HP are 1950cc. The 140 is 2044cc
I do not feel I need the extra engine volume. I certainly do not need the extra HP.
You are comparing the DF100 to the DF140 - I am comparing the DF100 to the DF70 /1300cc I had before.
I also prefer the lower rated 100 for the given cc for less stress and greater fuel efficiency.
As highlander and beene have already said the 26M is not a typical planing power boat hull and behaves differently thus power requirements are different too.
I personally feel that I will not have to go above 1950cc - 100HP. I will know when the motor is on the stern and the boat is on the water.
That moment will come soon and I shall keep you all informed.

Thanks for your input.

Octaman