Thanks for the feedback, does anyone know the weight and more importantly KW rating for a 26X transom. There's nothing in the owners manual and most of the info I can find is from the states and is sum what fuzzy.
I would doubt if MacGregor have ever published anything more technical than their recommended max. power rating for the engine (50HP for 26X, 60HP for 26M). I'm sure you can safely push it beyond that, how far is a matter of judgement - and at your risk! The actual stresses will very much depend on how you handle the boat.
Also of course consider your insurance policy.
—
Rick Jones (Treasurer), former 26X & 19 owner, Isle of Wight
I would have more reservations about increasing the weight of engine rather than the increase in power. If you can find a similar weight higher power engine you should squeeze a little more performance but (and it is a big but):
1. The speed to power is a very non linear relationship so going from 50HP to 90HP (+80%) will likely yield only +10 to 25% in top speed.
2. Given that modern IC outboard engine efficiencies are fairly similar +80% power will cost around +80% in fuel consumption (presuming you make use of the power).
3. Engine efficiency also drops off badly at lower revs and power levels so trolling with a big engine will be significantly more thirsty.
4. So you need to carry more fuel for the same range (yet more weight).
5. The planning performance of the hull is very dependant on weight distribution so a heavy engine will need higher speed before getting up on the plane.
6. Any extra weight will also raise the waterline, increasing the wetted area (reduced length:displacement ratio), in turn reducing sailing performance.
7. Additional weight aft has an unsettling effect on sea kindliness. The additional inertia aft moves the centre of rotation aft so that for a given wave height the bow raises more i.e. the boat pitches more as the aft squats into the waves then slams more as the bow drops further. The further aft the weight is the greater the moment of inertia (the outboard is about the worst case).
Roger Macgregor did a very good job of balancing the hydrodynamics of the Mac design. My best guess is 60HP is about the useful limit for a 26X.
Thanks for the feedback, does anyone know the weight and more importantly KW rating for a 26X transom. There's nothing in the owners manual and most of the info I can find is from the states and is sum what fuzzy.
David (Marmite)
Hi David
I would doubt if MacGregor have ever published anything more technical than their recommended max. power rating for the engine (50HP for 26X, 60HP for 26M). I'm sure you can safely push it beyond that, how far is a matter of judgement - and at your risk! The actual stresses will very much depend on how you handle the boat.
Also of course consider your insurance policy.
Rick Jones (Treasurer), former 26X & 19 owner, Isle of Wight
I would have more reservations about increasing the weight of engine rather than the increase in power. If you can find a similar weight higher power engine you should squeeze a little more performance but (and it is a big but):
1. The speed to power is a very non linear relationship so going from 50HP to 90HP (+80%) will likely yield only +10 to 25% in top speed.
2. Given that modern IC outboard engine efficiencies are fairly similar +80% power will cost around +80% in fuel consumption (presuming you make use of the power).
3. Engine efficiency also drops off badly at lower revs and power levels so trolling with a big engine will be significantly more thirsty.
4. So you need to carry more fuel for the same range (yet more weight).
5. The planning performance of the hull is very dependant on weight distribution so a heavy engine will need higher speed before getting up on the plane.
6. Any extra weight will also raise the waterline, increasing the wetted area (reduced length:displacement ratio), in turn reducing sailing performance.
7. Additional weight aft has an unsettling effect on sea kindliness. The additional inertia aft moves the centre of rotation aft so that for a given wave height the bow raises more i.e. the boat pitches more as the aft squats into the waves then slams more as the bow drops further. The further aft the weight is the greater the moment of inertia (the outboard is about the worst case).
Roger Macgregor did a very good job of balancing the hydrodynamics of the Mac design. My best guess is 60HP is about the useful limit for a 26X.
Just my thoughts, feel free to prove me wrong.
Dave.
Dave Newton Sailbadthesinner
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