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Twin 225's height v Mercs

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Rtant

Member
Guys,

The recent posts from Beantown and Metal-Chicken have led me to post to see if anyone has any experience with replacing Honda's from Mercs:

Trying to dial in my pair of 225 Honda's on a back of a 29 foot RIB. Giving us a right headache. Where a pair of Mercury's would just bolt on and go we are getting chine walking. We are up at 50 knots and lifted the Honda's as much as possible without a jack plate (fitted bobs nose cones to prevent water intake issues). The lifting and the nose cones helped but the walking / rocking is still there. I can see the inside cavitation plates and they are clear but i suspect the outside plates maybe catching the water (will be fitting a camera next time to check). All rather odd bearing in mind that Mercs have been fitted to the same model boat without any issue. I assume the Mercury's have the same setting out dimensions from transom bolt holes to prop, we are using 25'' legs? Worth noting the Honda engines rock around quite a bit.
Also i wondered if the Honda's saddle differs to the Mercs perhaps softer giving more play?

Anyway any info would be appreciated.

Next step is to get video footage of the outside cavitation plate and going to measure a Mercury 25'' from transom bolts to prop and cavitation plate to see if there is any difference with respect to the Hondas.

Suspect jack plates will be needed to raise the engines?

BTW Beantown please have another go with publishing your book....

Thanks
 
Thanks Chawkman good to see others are in the same ball park and successfully make it work. I note they also use Mercury and Johnson - wonder if they found any set up differences?
 
Hi Rtant.
Can't help with your problem as I'm a single engine guy but wanted to say hi from another Brit.
I'm guessing you're south coast, I'm Chester but have a place in abersoch which is where I get to play on our whaler.
We've got a Bob's hydraulic jack plate and it really does give you a lot of options. Hope you get the setup fixed without having to resort to more expenditure.
 
Thanks metal-chicken, good to hear and beautiful part of the word, the boats in Southampton, i'm in London. Interesting to hear you have a Jack plate, any reason why and do you find it useful?

I have found so many 'opinions' on jack plates and Honda's for that matter, not performance engines, don't like jack plates and the offset results in lifting even higher etc etc so its great to hear i am not on my own following this.

Was going to go with bobs Jack plate but need a pair which would mean two controls and dials (little room left on my dash!). Found Seastar do a dual control that i liked, they also have a function where it returns both to a pre set height which i thought was good. Bob's also do one large plate for two engines but was worried about reliability. The reason i have two engines is to give some redundancy. My plan is to eventually have the boat in Greece for island hopping.

The thing that worries me slightly is jacking these engines high could result in an unstable boat due to lifting the center of gravity - have you experienced anything - how big is your Whaler? My RIB is 2200kg with engines but no fuel and 29 foot long.
 
Actually we bought the Whaler s/h from a guy on West Mersea Island..... he'd bought had it put on. I think it's really good actually as you can get into shallower water and never worry about whether you've got the engine mounted at the right height!
The only downside is that it pushes the weight of the engine 6" back.

Ours is a 21@ Outrage and I don't see any issue with lifting the C of G...... we're only looking at 6" after all! I think the Bob's plates have a pretty good reputation and they are fairly simple things. I would have thought that one switch could activate both pumps.
 
Good point about the shallow water, i'm tempted to go with the 4'' set back.
Bobs have good customer service and i asked the same, due to two different pumps they can't keep the rams in sync with just one switch, they need feedback. The Seastar have a feedback 'measure stick' they call it - looks good but i guess another box of electronics......
Its a 6 week lead in time - perhaps i just get on with it - its not an insignificant amount of money tho....
 
Maybe it has something to do with the props. A 3 blade vs a 4 blade will ride different at higher speeds. I seem to remember talking props with a person several years back and he said cupping of the prop can create lift as well.
 
Thanks Gentilebrian, i'm using 3 blade i'll check what the merc's have on them perhaps they are providing lift.... so many variables!
 
Thanks Gentilebrian, I see what you mean. Questions have been asked. Will report back after i have gathered more information.
 
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