535 top speed

[CaptainPhaff]

Hi all, I had my first really good run out in Falmouth harbour this weekend, lovely and sunny but a bit of a swell to keep things interesting. However, I can't help thinking that my engine is not giving its all though.

It's a 1990 2 stroke mariner 60hp on a 535 and my GPS was reading about 23/24mph at the top end. Against the wind and the tide through some small waves it was reading nearer 12-13 mph. I don't have a rev counter to go by and I have only had the boat a couple of seasons so my experience of how it should run is quite limited.

I would be grateful if others could indicate what sort of speeds they get with various engine sizes. We were two up, both about 11/12 stone and a few bits and bobs on board but not weighed down too much. I don't mind pottering about at lower speeds but I would like to know what she should be capable of to give me something to aim for when trying to optimise the engine performance.

Thanks

[bobtooke]

With my previous engine, a 35hp Johnson, I used to get around 18-20 knots (20-22 mph) and with my new 50hp engine I get about 28-30 knots (30-33 mph) so I think your 60hp is underperforming to what its capable of.
Of course, a swell will slow things down but even in a good swell I can plough through at 18-20 knots though it will slam a bit so I usually throttle back to about 15-16 knots.
If yours seems to be running smoothly and its never been any different, the chances are, its the prop size need attention but you'll need a tachometer to work out the correct size.
To give some sort of broad idea of sizing, I'm running a 10.5 x 14 3 blade prop on my 50.
Hope this helps a little.

[IlsonMark]

With my 70hp 2-stroke Johnson I usually get around 28 knots. Interesting that Bobtooke is getting more with his 50hp.

Guessing that my old engine from 1980 has lost a bit of power over the years!

[Deleted User 5743]

If you can't get it to plane then that could be about right. Weight balance makes a big difference as I've learned.

[CaptainPhaff]

Thanks for your responses, time to look at what to do next. Having done 10 mins googling I have realised that propellor sizing is a whole new science that I will need to learn. Any advice that people can offer on what prop size is ideal for a 2 stroke 60 hp motor on a 535 will be gratefully received. Thanks again!

[daveinglasgow]

Hi

ok top speed 36 with a new 60 hp 4 stroke

you speed is v low so......

1: check compression first. if this is low or different between the cylinders get rid of it quick
2: check your revs: you need 5800 to 6000 so if you are not getting this the prop is to big and if it stops going faster before this your prop is to small
3: on all small boats you must get the ballance right ie she needs to sit flat so I am guessing but move weight to the front or at least as much as you can

report back and let me know how you get on

Dave

[CaptainPhaff]

Thanks Dave, this is probably a daft question, but why do you say get rid of it quick if the compression is low or not balanced? Obviously it's not a situation that will improve but other than being crappy on performance is there another reason such as safety etc?

I can live with 24mph as I bought the boat a few years ago and it has only ever really performed at that sort of level so it doesn't bother me as I am more into pottering about getting to coves and beaches etc than zooming around at high speed.

Thanks
David

[daveinglasgow]

Hi

feel free to call but in simple terms it means reboring the power head soon and that is circa 1200 + as once its starts to lose compression they go pritty quick. This means in most cases that the cost to repair is simply not worth and hence if points 2 and 3 dont solve it then ooch. also remember that you are burning more fuel for the same speed .

Dave
0759 563 8185

[CaptainPhaff]

Thanks Dave, I will let you know how I get on with the compression and rev tests that you suggest. It will be a good few weeks before I have any updates as my boat is now on my Dads drive in Cornwall for the summer but I live in Worcester!

One question re the revs - will one of those cheapish digital tach's do the job or would you go for a more permanent analogue dial set up. If the latter, could you recommend one to go for on my engine?

Thanks David

[daveinglasgow]

Hi

I would get a second hand one of flee bay. Rev counters are vital . it shows if the prop is right, it shows if the engine starts to race, it shows if revs drop during a trip so its something that we should all have. there are loads around used so you will have no problem picking one up.