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Old 03 October 2017, 12:56   #1
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Bigger outboard restrictions

Hi all,

I'm considering upgrading my 2004 Honda 90 on my Zodiac Open Pro 550. It works fine, but feels like it is at the bottom end of capable - when pulling skiiers I have to start slow and build up, otherwise the pressure stalls it.

The original boat specified up to a 115HP, but here's my question...

What is the main factor driving the size of the engine the boat is capable to take?

Is it weight (in which case, newer engines may be lighter for the same, or larger HP)?

Is it torque on the transom - i.e. something too powerfull might overly strain the transom

Is it just the boat length limitations - i.e. no point in going above X as it would not go any faster?
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Old 03 October 2017, 13:01   #2
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There is no way you should be stalling with load.

What rpm does the engine reach?
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Old 03 October 2017, 13:25   #3
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What size prop you might be too high on pitch to pull skiers,are you saying the engine stops under load which isn't right
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Old 03 October 2017, 13:37   #4
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Sounds like bogging out when you give it a big handful, possibly a carb issue, fairly common on a carbed Honda
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Old 03 October 2017, 16:44   #5
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I'm guessing you're trimming it right down for the "deep start"?

I get the same problem if I do that with mine because it pushes the pressure relief exhaust ports on the back of the leg under the water.

Try lifting the trim until the ports stop blowing bubbles
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Old 03 October 2017, 17:12   #6
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I'm guessing you're trimming it right down for the "deep start"?

I get the same problem if I do that with mine because it pushes the pressure relief exhaust ports on the back of the leg under the water.

Try lifting the trim until the ports stop blowing bubbles
Surely there has to be an underlying problem there if you can't power on without bogging out? I doubt the manufacturer made an engine you can't accelerate unless trimmed out
You would always trim in for best hole shot
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Old 04 October 2017, 02:37   #7
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Surely there has to be an underlying problem there if you can't power on without bogging out? I doubt the manufacturer made an engine you can't accelerate unless trimmed out
You would always trim in for best hole shot
It doesn't "Bogg out". It stalls before it comes over idle revs with the throttle wide. I've had it with a few engines...Evinrude, Mercury and the Honda.
It doesn't need to be trimmed out, just lifted off the bottom stop to relive the exhaust back pressure. Depending on how deep the engine is sitting the relief ports can be under the water.
I'd guess at 2004 his engine will be fuel injected as my 2002 one is.
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Old 04 October 2017, 03:47   #8
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It doesn't "Bogg out". It stalls before it comes over idle revs with the throttle wide. I've had it with a few engines...Evinrude, Mercury and the Honda.
It doesn't need to be trimmed out, just lifted off the bottom stop to relive the exhaust back pressure. Depending on how deep the engine is sitting the relief ports can be under the water.
I'd guess at 2004 his engine will be fuel injected as my 2002 one is.
So it's worse than just bogging out it actually chucks it at the critical moment? Sounds like a fault to me.
Not something I've come across unless there was a blocked jet or accelerator pump problem
Is this what's to be expected of a modern engine? Personally if I took delivery of an engine that behaved like that I'd be handing it back.
If the engine was fitted to a boat that sat deep in the water then relief ports would be underwater anyway regardless of trim.
Imagine a car that chucked it at the lights every time you floored it.

Anyone else experience this on a new engine?
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Old 04 October 2017, 03:58   #9
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OP. Does it do it all the time or just when you've got a skier(s) connected?
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Old 04 October 2017, 06:18   #10
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So it's worse than just bogging out it actually chucks it at the critical moment? Sounds like a fault to me.
Not something I've come across unless there was a blocked jet or accelerator pump problem
Owned 16 boats over the years and seen this problem on at least half a dozen of them with different engines. both fuel injected and carb'ed.

Only an issue with a skier on the back and easily worked around. A bit like dropping the clutch too fast on a car.....the engine revs are to low to to produce enough power to move the car, the throttle is wide open throwing air at an already lean engine and....it stalls. No big deal.

I'm guessing you wouldn't take your car back to the dealer because you stalled it?
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Old 04 October 2017, 06:24   #11
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Owned 16 boats over the years and seen this problem on at least half a dozen of them with different engines. both fuel injected and carb'ed.

Only an issue with a skier on the back and easily worked around. A bit like dropping the clutch too fast on a car.....the engine revs are to low to to produce enough power to move the car, the throttle is wide open throwing air at an already lean engine and....it stalls. No big deal.

I'm guessing you wouldn't take your car back to the dealer because you stalled it?
I started waterskiing when I was 14 I'm 53 now and still ski occasionally and never experienced this with a healthy engine
I'm saying no more as I'm aware of thread drift apologies to the op
Maybe Honda have a problem and your initial thought on upgrading is the correct way to go
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Old 04 October 2017, 09:10   #12
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I started waterskiing when I was 14 I'm 53 now and still ski occasionally and never experienced this with a healthy engine
I'm saying no more as I'm aware of thread drift apologies to the op
Maybe Honda have a problem and your initial thought on upgrading is the correct way to go
Thanks all contributing. The holeshot probelm is generally with Skiing only. I occasionally got this under general use when carrying 5-6 people, but a bit of servicing (MB Marine) seems to have improved that and it's now more about skiing. It's improved when fully trimmed in, but not removed.

Whilst this is a contributor to my consideration of a new engine, its not the only factor. Can we come back to the original questions on what factors control the maximum size of an engine on a boat like this?
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Old 04 October 2017, 09:19   #13
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It is many things if it is ce rated that are taken into account, don't know exactly what they are.

You would be wise to stay in the weight and hp limit stamped on your plate though.
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Old 04 October 2017, 09:45   #14
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It is many things if it is ce rated that are taken into account, don't know exactly what they are.

You would be wise to stay in the weight and hp limit stamped on your plate though.
Xk59D pretty much nailed it here all the info should be on the transom of a boat your age.
A few years ago overpowering boats was commonplace but in todays compensation climate probably wise to stay within the hulls recommended hp.
Obviously as close to the upper limit as practical is best for pulling loads.
Even if your a bit down on power for skiing your not looking for a high top end so maybe think about having two props a fine pitch one for water sports and a higher pitch one for general cruising then you have the best of both worlds
Maybe see if you can borrow a smaler pitch prop than you have and if successful buying a prop is way cheaper than an engine
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Old 04 October 2017, 12:10   #15
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What size prop you might be too high on pitch to pull skiers,are you saying the engine stops under load which isn't right
Prop size is the manufacture standard 19" - I did consider trying a 17" but generally don't swap / remove the prop and didn't really want to loose top speed.
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Old 04 October 2017, 12:13   #16
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Thanks, had considered this, and maybe the way to go, but was still interested in what drove the parameters for engine size. Clearly there are bigger HP engines at lower weight today than there were 13 yrs ago.
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Old 04 October 2017, 12:40   #17
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Thanks, had considered this, and maybe the way to go, but was still interested in what drove the parameters for engine size. Clearly there are bigger HP engines at lower weight today than there were 13 yrs ago.
The CE requirements for certification give fairly detailed calculations based on length beam tube diameter then a series of stability tests to arrive at the engines maximum allowable hp. Manufactures can recommend hp below the calculated max but not over as far as I'm aware. Although years ago 4 strokes were considerably heavier than now, at the time your boat was approved fairly lightweight 2 strokes were still available. It would be unwise to assume the rating was arrived at on the basis of a heavy old 4 stroke and think it acceptable to fit a lighter modern engine of hp greater than the plate specifies.
Whilst in most cases overpowering would probably be fine the problem will arise if or when you try to make an insurance claim
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Old 04 October 2017, 13:24   #18
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I have a Zodiac 530 pro from 1988 when the light weight 2s were king, plated at 120hp max with no max weight. The 115/120hp 2 strokes of the time were about 120-140kg. I did lots or research into other boats of the same model and their engines and found some older 4 strokes up to 180kg on them, or twin 60s which were pretty heavy. In the end I bit the bullet and got a merc 115 at 163kg and the boat hasn't fallen apart. It also still sits nice and level. Top end is a little more but hole shot is so much better than with the poorly tuned 75hp I replaced. It currently runs a 17" prop. I could probably get a few more mph (tops at 42mph) with a prop swap but it chine walks anyway so not too bothered.

Another option for improving your existing setup could be a different prop material or design, e.g. stainless or 4 blade. I really don't know much about prop changes but I'm sure stainless props can help holeshot without loosing top end (somebody please correct me). I think some 4 blade props (spitfire?) will do the same.

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Old 04 October 2017, 14:03   #19
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Thanks, all good info. Surprised your 530 has a bigger hp allowance than my 550, but I guess regulations change.

I will look more into prop options. I did look at this a couple of years ago, but perhaps time to try.
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Old 04 October 2017, 14:04   #20
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Thanks Beamishken very useful info.
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