More top end?

[Limecc]

Chipko raises a valid point here about the ISO hole pattern.
I did make the assumption the Yam 25 had this but it hasn't. Strange because my Merc 30 did and that's in the same 25/30hp class. Maybe there was no standard that far back?

I'd consider making some sort of adaptor to raise the transom or convert the Yam saddle to ISO pattern. Not an option for everyone who might not have skills or facilities, but I feel it would be worth it.

[chipko]

Jeez. You just don’t let go do you.
Let’s face it your advice is totally irrelevant to a small lightweight rib and portable outboard combo.
You have a nice day Matey!

[Limecc]

Originally Posted by chipko

Jeez. You just don’t let go do you.
Let’s face it your advice is totally irrelevant to a small lightweight rib and portable outboard combo.
You have a nice day Matey!

Very very nice thanks!

More seriously, I'd just have to know. I wouldn't take your word even with all the experience you have unless you did the trial and error with this particular hull. You did a nice job lowering the cheap Cat transom. Shame it didn't work out. A risk I'd have to take also.
Poor man’s cat

P.s. you're the pit bull. Very aggressive.

[beamishken]

Originally Posted by Limecc

Very very nice thanks!

More seriously, I'd just have to know. I wouldn't take your word even with all the experience you have unless you did the trial and error with this particular hull. You did a nice job lowering the cheap Cat transom. Shame it didn't work out. A risk I'd have to take also.
Poor man’s cat

P.s. you're the pit bull. Very aggressive.

I actually agree with you, if you lift the engine a little & dont get the av plate high enough that its above the water flow your not making the best gain. Getting the av plate above the water flow will remove way more restriction than just a few mm which you'll probably hardly notice any gain

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[Fenlander]

The science and theory is handy to have in the back of your mind and I usually do but in 14 smallcraft under 5m... 10 of them SIBs 3.8m or less... and powered by 12 outboards of 20hp and under all I've done is hung the outboards on with no more than a 10-15mm packer under the saddle judged by eye** and they've performed fine with just occasionally a prop pitch change dictated by actual testing using a small tach. To be honest 90% of the time sea conditions are the limiter on speed for a SIB or medium V SIB sized RIB rather than the Nth degree of setup tuning.

Worth mentioning I've found significant differences in performance related to pitch between brands and their differing blade styles. So if you are working through a theory of what change you'll see it may not translate in practice if you change pitch and brand/type at the same time.

** Some folks may wonder why then I've been involved with significant transom raising on the Aerotec but that was all about splashback rather than speed.

[The Gurnard]

Yup..I agree with you Fenlander and I also think Chipko was bang on the button with his guestimate of AV height vs performance

I have first hand experience of the Alu Hull Ribs in question..so here facts for my outfit .. (all outfits of same hull could be slightly different depending on layout and OB or prop make)

AV plate level to transom base with 10mm packing, in comparison to no packing and AV 10mm below .. I gain only one mph but pay the price of a little cavitation on corners.

With 20 mm packing piece which is the max packing I can go .. which puts AV plate 10mm above transom level .. the prop is very obviously slipping when accelerating and much more cavitation on turns...so totally unsuitable for my setup and use

In the end ..as I hate cavitation .. I left it without packing.. AV plate 10mm below transom .. thats my choice going by my experiments...and Im delighted with it

[chipko]

Hey Donny, was quietly hoping you’d surface at some point as a seasoned Quicksilver 420/25hp Captain and welcome your findings, as always.

After sticking my ‘head above the parapet’ and getting well and truly shot down, comforting to hear your thoughts. [emoji106]

[The Gurnard]

Hi Chipko ..I can only apologise for not joining in earlier...I did write a reply but then decided to let the theard run as I found it amusing..especially when the Transom Template was posted as we both know portable outboards have no standard..in fact my mariner 25HP has only two security bolt holes ..

Hoping to get my new Yamaha 25HP fourstoke next month so will video it getting set up for proof. It would be a real shame if anyone Drilled their transom because of Boat Bollox talk ..then find it was utter crap !!!!

[jeffstevens763@g]

Originally Posted by chipko

Hey Donny, was quietly hoping you’d surface at some point as a seasoned Quicksilver 420/25hp Captain and welcome your findings, as always.

After sticking my ‘head above the parapet’ and getting well and truly shot down, comforting to hear your thoughts. [emoji106]

Agree don’t think you were shot down chipco some ignore the basics and go over the top which you pointed out but the handbag came out to accuse you of aggression which is not at all helpful to the OP, sadly the forum tends to go down this route on some threads shame really.

[chipko]

Thanks Donny and Jeff. Hopefully this info will all be useful to the OP and save a peppered transom.

Donny, looking forward to your reviews of the Yam 25…an absolute peach of a motor from what I’ve heard. Not jealous at all, at all. [emoji3]

[jeffstevens763@g]

Originally Posted by The Gurnard

Hi Chipko ..I can only apologise for not joining in earlier...I did write a reply but then decided to let the theard run as I found it amusing..especially when the Transom Template was posted as we both know portable outboards have no standard..in fact my mariner 25HP has only two security bolt holes ..

Hoping to get my new Yamaha 25HP fourstoke next month so will video it getting set up for proof. It would be a real shame if anyone Drilled their transom because of Boat Bollox talk ..then find it was utter crap !!!!

Nice one mate.

[Windsurfer]

Thanks everyone for your reply’s, had a great day tinkering yesterday in the sun.
Did my first service, plugs, filter ,impeller,gear oil, impeller , prop, I used to mess around with motocross bikes in my late teens / early twenties so it’s been awhile since I’ve got my hands greasy.
Really enjoyed it to be honest, tea on tap passed out the window and my youngest hitting everything with his plastic hammer (there was only a few swear words).
Wasn’t sure about doing the impeller but it went really well , I could tell the outboard had been very well maintained previously the hardest part was changing the fuel filter as it was so tight to undo.
I may have been a little ott cleaning and greasing but I’m sure I’m not the only one that’s formed a strange obsession for there outboard.

After a long while staring at my outboard and transom waiting for my brain to kick in,I’ve decided I’m going to remake a inner transom plate (probably out of a plastic chopping board) slightly larger than the existing one, screwed into the existing holes.
This will then give me a safe clamping range from AV to Hull of minus 20mm (current position ) up to about plus 5mm.
I can then test to my heart’s content with a couple of packing pieces and no harm to the transom will be made ! My tachometer as also arrived so this will be fitted today then I can report back with some figures and hopefully I’ll have an excuse to buy a shiny new prop!
Stay positive people

[Scooby]

Keep me posted on results please I'll hopefully be out testing next weekend just need to wire it up to charge the battery

[Fenlander]

A shiny new prop is always good... but if thinking aftermarket do cast an eye over post #33 on this thread where I tested 4 props on a 15hp Yamaha and found the aftermarket brands had pitch inconsistency.

https://www.rib.net/forum/f36/yamaha...ice-81611.html

[willk]

Originally Posted by Windsurfer

I’ve decided I’m going to remake a inner transom plate (probably out of a plastic chopping board)

Those yokes are generally made out of nylon and as slippy as hell. I tend to associate high grip materials with securing engine mounting screws...

Stainless chequer plate is equally guilty of slipperiness, in case you plan to use it instead.

[Windsurfer]

Originally Posted by Fenlander

A shiny new prop is always good... but if thinking aftermarket do cast an eye over post #33 on this thread where I tested 4 props on a 15hp Yamaha and found the aftermarket brands had pitch inconsistency.

https://www.rib.net/forum/f36/yamaha...ice-81611.html

Thanks for the heads up , great thread that !

[Windsurfer]

[QUOTE=The Gurnard;850210]Yup..I agree with you Fenlander and I also think Chipko was bang on the button with his guestimate of AV height vs performance

Great to get some feedback from someone with the same model of boat!

Funny I was watching this video of a chap servicing his outboard on YouTube the other day , pretty sure it was you

[Windsurfer]

Originally Posted by willk

Those yokes are generally made out of nylon and as slippy as hell. I tend to associate high grip materials with securing engine mounting screws...

Stainless chequer plate is equally guilty of slipperiness, in case you plan to use it instead.

Great point thanks , I could just move the existing plate up but would mean drilling a few more holes in the transom not the end of the world but if I had a larger plate I could just screw into existing holes.
I’m sure the existing plate is aluminium, so I guess I just needed to get a larger piece of aluminium with texture or bubbled on one side would do the trick?

[Highland Haggis]

Wow this thread is interesting my thoughts are with Donny on this he’s a well seasoned boater and has years of experience with his outfits.
His knowledge is worth listening to und taking note of [emoji6]
Finally he’s getting a four stroke wow he’ll be going round Ireland with his fuel economy [emoji41]

[beamishken]

Originally Posted by Highland Haggis

Wow this thread is interesting my thoughts are with Donny on this he’s a well seasoned boater and has years of experience with his outfits.
His knowledge is worth listening to und taking note of [emoji6]
Finally he’s getting a four stroke wow he’ll be going round Ireland with his fuel economy [emoji41]

The question was more top end? Not what is best compromise for your set up though

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