Re-powering a MacM from 70 HP up

[Gypsy]

True planning is more than just lifting the bow , it is also lifting the stern , as well .
If you apply enough power to a displacement hull , you will push some air under the bow and it will lift . With the bow lift , comes the stern bury , pushing the stern deeper in the water and creating more drag.
This also explains the huge wakes from sport fishers and high speed trawlers .

Add even more power and you force enough air under the hull to actually lift the stern , now the entire boat is sitting on top of the water and ready to go fast as the drag has greatly decreased .

Powerboaters call this the breakover point , thats when the stern lifts and settles the bow back down.
I have never seen a picture of a MacGregor truly planning . To truly plane a Mac , it probably would require a 125 hp motor or modifications to its trawler hull . Either one would then affect its sailing abilitys.

I am one of the rare Old Salts that went from 30 years of powerboating to sailing , so I know a little of what I write.
What I love most about my is its ability to pass a gas station . A trait my 220hp Bayliner couldn't do !

[vkmaynard]

Actually Gypsy hitch a ride on a 90 Hp X and you see that is exactly what it feels like. For the bow to settle down the transom has to lift otherwise that would imply the entire boat is sinking lower in the water at speed. The wake moving backward past the center of gravity of the boat is what causes the bow to drop or pivot down.

Victor

[Gypsy]

Actually Gypsy hitch a ride on a 90 Hp X and you see that is exactly what it feels like. For the bow to settle down the transom has to lift otherwise that would imply the entire boat is sinking lower in the water at speed. The wake moving backward past the center of gravity of the boat is what causes the bow to drop or pivot down.

Victor

Basically what I said , but you said it a little more techinically When the bow settles back down , the stern rises , now the entire length of the boat is higher in the water .
But what I have seen is the bow is raised , but the stern is deeper . It hasn't reached the breakover point and isn't truly planning . The entire boat isn't sitting deeper , but at an angle .
You call it the wave moving back , I call it forcing air under the hull . when the air gets under the stern , it raises , achieving true plane.

Perhaps a 90hp will accomplish this, I haven't seen it.

[Divecoz]

How about Highlanders Videos? Is his boat on plane?

[Gypsy]

How about Highlanders Videos? Is his boat on plane?

Post the link you are talking about .

[beene]

http://www.youtube.com/user/Pegasus26M# ... LpPhSBsx3c
http://www.youtube.com/user/Pegasus26M# ... rNpfC5JYQg
http://www.youtube.com/user/Pegasus26M# ... vBXHI8uQgw
http://www.youtube.com/user/Pegasus26M# ... Bn47Z6U9HE

G

[kadet]

How about Highlanders Videos? Is his boat on plane?

Even the experts cannot definitively agree on what true planing is but!

IMHO almost but not quite as half the hull is still in the hole with a nose up attitude. Considering there is no chop on that water look at the size of the bow wave being produced, a significant % of the hull is still displacing a lot of water.
Given the hull shape of the and the compromise between sail and power it may never make it to a true plane, but if you are going 25 knots and still not 100% up on a plane who cares apart from the fuel bill

[Gypsy]

it is hard to say from the videos , but , to me , the stern doesn't look much higher in the water.
It looks like its sitting near to where it would , at rest.

On my Bayliner , we had a full width swim platform . At rest the platform was a few inches above the water . Going on plane , the platform dragged in the water . On plane the platform was a foot or so above the water. This kind of stern rise doesn't appear to be the case with Peguises .

While on plane the Bayliner was almost level from bow to stern , Peguisis is bow high.
This kind of stern rise doesn't appear to be the case with Peguises .

As Kadet said He is going fast , but a trawler can go that fast as well , with enough horsepower pushing it. In comparision to my Bayliner , I don't think He is truely planning.

I wonder what effect trim tabs would have on a Mac ?

[blue angel]

DaveB: unless you want to go really biggier and heavier, I think I too would consider the new yamaha 70 and new suzuki midsize (70?). but with more yamaha dealers in florida, that might be part of the decision. the yamaha 60 i have I am happy with, hi thrust gets about 18 knots at sea level, the newest 70s migiht be a bit faster and no heavier, or maybe not that different??? by the way how to do you like cape coral. looks like one the cheapest places to buy a house with a sailboat lift out back?

[Highlander]

Hi All

Well for starters the M Hull has a 15 degree dead raise to a rounded hull at the sides no strakes or hard chines, no soft chines like the X Hull. Also the most aft section "transom" of the M Hull is narrower the water line at the transom is I beleive only 6" I did not have time to measure it this morn.So this is why you see what apears to be alot of water being pushed aft & up against the Hull their is nothing to push the water out & away from the Hull thus exposing a Planing Hull so the Hull looks like it is semi-Planning or displacing water , In one of my Vids you can clearly see "Beene's" rudder brkts exposed & they are below the water line when the boat is idle so this means their is only about 20-24" of stern "transom" in the water the rest of the stern on both sides is covered with the spray of water coming back from the wake also notice that when Beene was at W.O.T. his boat is almost level he was pulling back on the throttle most of the time as he was running a 15" prop to my 14" prop . what a difference that makes " I'll be buying one this yr as I am running 6500rpm @ W.O.T with my 14" prop & thats even with being heavely loaded
J
PS Gazman installed spray rails on his X . but they are pricey I bet on an M Hull they would show the Hull fully planing !

[Highlander]

On a note
Was at the boat show on sat. seen these nice small gas strut controlled trim tabs . push down to release pull up lockin the up possition will up-date later when I get more info on them this sat

J

[Gypsy]

On a note
Was at the boat show on sat. seen these nice small gas strut controlled trim tabs . push down to release pull up lockin the up possition will up-date later when I get more info on them this sat

J

Trim Tabs make a world of difference in how much speed is required to go on and stay on plane .
In my Bayliner , trim tabs , fully down , I could maintain a genuine plane at 18 - 20 mph .
Not using the tabs required more throttle to get on plane and higher speed to maintain planning.

If trim tabs could be installed on a Mac it would probably be the boost that makes it truly plane.
It might be the difference that makes the boat breakover and get air under the stern area of the hull.

[waternwaves]

I dont mean to be a sap and tell people what they think.

however,

lets not forget geometry,
Lest your eyes decieve you.
high speed powerboats typically have flat bottom surfaces that have a V cross section and roughy the intersection of two planes in the rear of the boat. this "normal" to most geometry is not what decides whether or not a body is planing,

the mac does not have this
in fact, x boats definitely and m boats to a lesser degree have compound curved surface that rises toward the transom.

with a large enough horsepower engine, (most cases 90 with the correct prop) the contact area, the mac hull is travelling at a similar angle to the ski boat, all other things being equal, it is just that that surface is curved relative to the mac gunwhale, and the mac rides a a different relative boat angle. ( in fact to be technically proper we should not even call the aft surface of a mac a 'Plane".


When you are riding next to a mac (10 ft away or so, it is clear the boat is on top the water and planning), the reason most people do not think of it as planing is because most are only familiar with conventional ski boat type operation. Their eyes are decieving them. Putting a curve on the rear surface of the boat fools the eye, but doesnt change the physics.

IF you want to plane the MAC, AND ride almost level, and convince the remaining % of people you would have to add even more horsepower to push the nose down, or a control surface to direct water downward to raise the sterni.e trim tabs) (also requiring more horsepower.
(I dont think I will see 50 kts on water for a mac in my lifetime.........(john, that is not a challenge)
but one ride along side the boat at 24 kts clearly shows it is planing.

And I for one can agree that the double compound curve bottom of the X is not a candidate to go much faster, it does not track well even with more power.


If you want it to ride more like a ski boat, add tabs and horsepower and a little keel, and and then sail slower...........


Did I read that higlander will have a full time admiral??????

[Gypsy]

When you think of planning , I think of the bass boats , so common in the southeast . They are flattened out vee hulls , with humoganus engines on them. They are nearly all 2stroke for more pwer , and usually 200hp or more on a 20 foot lighweight hull .
When on plane these boats have about 2feet of the stern still in the water , the rest of the boat is airborne.
When my Bayliner is on plane the boat is out of the water up to about midship , under the driver is about where the hull meets the water . The swim platform is about a foot above the water , the only part of the motor in the water is about from the cavitation plate down.

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

[bscott]

The slight rocker in the aft of the is Roger's attempt to lift the stern to reduce drag. Racing J24s and Capri 25 we always placed the crew as far forward as possible (even down below in the cabin) to raise the stern out of the water when on a down wind tack.

I don't think it matters if the Mac ever obtains a true plane as long as the owner is willing to spend big boat bucks to go fast and have fun

Bob