Need help choosing engine

[vann]

Hello,
I am buying a new Mercury engine and I've a really hard time choosing between 15 and 20hp. My boat is originally 4,00m but I recently extended it to 4,5m, which barely increase it's weight. Everywhere I read about the difference between 15 and 20 hp I find that 15 hp are really 19hp and that they are both built on the same platform which suggests similar performance. I also read that Mercury's new 20hp 4strokes are revolutionary and I'm confused now.
What I need to know is if there is a big enough difference between the two which is worth the price difference, or it's more a label than a performance issue.

 

[rafiki_]

Sorry, can't help personally on this, but have you tried talking to Mercruiser, or Barras, the importers? I expect they will be able to give the techie info you seek.

 

[Nick_H]

I can't believe Mercury's 15 hp is really 19hp straight out the box, or they'd open themselves up to all sorts of legal claims. It's quite possible that the 15hp and 20hp are the same basic engine, so the 15hp could be modified to make it 19/20 hp, however it's often easy to find people who will tell you about this, but much harder to find someone who will do it.

I'm struggling to think of a 4m boat that wont handle a 20hp outboard, so you're unlikely to be overpowering it. If it's a planing boat, then the 20hp is likely to be an advantage. If it's not a planing boat, then the extra 5hp may achieve little or nothing. We need a bit more info really, especially what type of boat it is.

Oh, and distributor is EP Barrus, not Barras, in case you wanted to google it.

 

[PaulGooch]

It may well be the case that the 15 is the same engine as the 20, but restricted. Merc/Mariner do this with several engines, the 4/5/6hp are all the exact same engines, but with different carbs.

If the boat is a planing hull the extra power might come in handy. It's often more economical to fit a bigger engine and run it at lower RPM, rather than fit an underpowered unit and run it flat out.

 

[vann]

It's a planing boat and it's planing with a 20 years old(maybe more) 25hp rusty Johnson(who knows if it's still 25,by the sound of it it's not going on full RPM) with 3 adults on board.
I am aware I can't go wrong with the 20HP but money is an issue here.

 

[vann]

btw, thank you for the info on the importers but I don't live in the UK.
Point taken tho

 

[Nick_H]

A 15 looks mighty small for that boat, but I don't know much about these hulls so others may say it's OK. The 25 that's on looks a much better match though.

 

[PaulGooch]

It's a planing boat and it's planing with a 20 years old(maybe more) 25hp rusty Johnson(who knows if it's still 25,by the sound of it it's not going on full RPM) with 3 adults on board.
I am aware I can't go wrong with the 20HP but money is an issue here.

If the old Johnson is a 2-stroke, be aware that the engines you've mentioned will be much heavier. Therefore, a new 25hp 4-stroke may well not perform as well as the current engine (depending on how much down on power it is).

I understand that money is an issue (it always is), but fitting an underpowered engine now will cost you dearly in the long term.

 

[vann]

Many thanks for the opinions!

 

[andyc]

Yep a 4stroke engine at 15hp will weigh the same as a 25-30hp 2 stroke which will make a big difference in weight distribution and getting on to the plane.

I have a 4hp suzuki 4 stroke and it weighs the same as my mercury 15hp 2 stroke.

I will say, My 4 hp is the same engine as the 6hp.Only difference is a small throttle restrictor on the carb that has 4hp stamped on it.I bent it and it now revs higher which is how they get the extra power,more revs.

Id go 20hp 2 stroke.light and more powerful and will get you on the plane when heavy better than a15hp engine.