20" on 25" transom?

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    Posted: 09 Sep 2021 at 1:51pm
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Im wondering..
Take say a 6m Ramco or similar 'podded' set up hull set up for a std 25" outboard.
 Could, can a 20" V6 150 johnny be fitted or adapted to fit?
And If so is it practicable to do so?
 Thu may mean bit of cutting welding of the pod?

Reason I ask is looking at buying bigger boat... Our current commander (20") transom has a the 20 " johnny on it.

Its not a biggie to fit plates or modify the transom to fit a 25"

If brought a boat that had say a 115 hp.. which still powers the commander fine, I swap the 115 for our current 150.hp.

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Post Options Post Options   Likes (0) Likes(0)   Quote Fraser Hocks Quote  Post ReplyReply Direct Link To This Post Posted: 09 Sep 2021 at 2:08pm
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With a jackplate maybe? I know that's a big motor, but in the states they seem to do that kind of thing a lot with big motors. Might not be a cheap jackplate, but if it was a hydraulic version you would have the luxury of jack motor trim as well 😊
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Post Options Post Options   Likes (0) Likes(0)   Quote MATTOO Quote  Post ReplyReply Direct Link To This Post Posted: 09 Sep 2021 at 5:04pm
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I suppose you would need to access why there is a difference between different leg lengths.

Then understand how your transom construction works with those different leg lengths.
Just cruising in my now sweetas pimped out Southern 755 HT0!
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Post Options Post Options   Likes (1) Likes(1)   Quote Kandrew Quote  Post ReplyReply Direct Link To This Post Posted: 09 Sep 2021 at 5:32pm
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Yep and I would have thought with your years of propping boats and offering information on repowering boats that you might have seen what happens when use a 20” on tinny with a pod, the motor sits way too low and in big swells like you get on the west coast and the motor will get dunked. Motor might be to heavy as well.

You could swap the leg on your 150 to long shaft and look around for a short shaft for the 115
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 10 Sep 2021 at 9:32am
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Titanium
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Yep and I would have thought with your years of propping boats and offering information on repowering boats that you might have seen what happens when use a 20” on tinny with a pod,

 Why such a comment? you of all ppl would know one doesnt need to spend yrs on 100s boats to do propping, in fact you know very well, one doesnt even need to see the hull..just have built data base from previous similar hulls to establish coefficients for formula

 There is this thu

You could swap the leg on your 150 to long shaft and look around for a short shaft for the 115
I have not seen a 20" leg on a 25 " transom or pod.. And I do not think many have. Therefore the effects of what could be is assumption based on sketches playing with dimensions
 Hence why Im asking , maybe someone who fits engines, or has done it .. or not because off.. Im asking.

It is Covid L4 so I cant simply head off down the road an check out how a ramco or similar boat has the pod fitted, how bult , if could be modded ...

 I would with your experience you could have given some constructive insight, rather than a -ve response,  totally sarcastic unconstructive response

You could swap the leg on your 150 to long shaft and look around for a short shaft for the 115

 You will know the availability of suitable legs, the cost of them, then, that on top of the cost of the project of buy another boat , set up both, then re sell .. would not be cost to viable.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 10 Sep 2021 at 9:40am
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Mattoo;
I suppose you would need to access why there is a difference between different leg lengths.

 Yes thats  sort of sorted.. I think.. so still maybe bit research to do there.

Then understand how your transom construction works with those different leg lengths.

Being Covid L4 getting to actually climb around a few hulls, pods, measure up, figure out if can be modded , cant be done atm.

I wonder if anyone has a close up that shows the actual construction of a few of these pods... cutting down transoms just doesnt look commomsence and measuring (as against assuming) seems to confirm.
 
With pods being further  out from the rear of the bottom of the transom/ keel.. means engines sit higher than if on the actual transom... due to the elliptical curve the water comes out from under the keel to reach normal  'sea level'
 It is this that has me thinking about cut down pod to 20" leg ???
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Post Options Post Options   Likes (1) Likes(1)   Quote Kevin.S Quote  Post ReplyReply Direct Link To This Post Posted: 10 Sep 2021 at 11:54am
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I think going that way could be tricky.  Fitting a 25" OB on a 20" hull means building up the transom to increase the engine height, which is often possible (I've done similar myself).  But fitting a 20" OB on a 25" hull requires you to remove 5" from the transom to drop the engine to the right height.  Depending on the hull design that could cause problems.  Adding a pod on the back should make it possible, but that's a lot of work compared to just buying a boat with the right OB and selling your current boat as is.
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Post Options Post Options   Likes (0) Likes(0)   Quote Pcj Quote  Post ReplyReply Direct Link To This Post Posted: 10 Sep 2021 at 2:27pm
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There you go "steps" sorted

https://www.trademe.co.nz/a/motors/boats-marine/motorboats/listing/3056515681?bof=Wuef94xS

Have googled ramco 6m and all have 115hp  must be a reasonSmile
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 10 Sep 2021 at 4:44pm
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KS
I think going that way could be tricky.  Fitting a 25" OB on a 20" hull means building up the transom to increase the engine height, which is often possible (I've done similar myself).
Yeah went right into that with our current hull a few yrs back when looking (and did) re powered.. Its not to expensive and actually rebuilding our transom  not a biggie, home work done on that part.


  But fitting a 20" OB on a 25" hull requires you to remove 5" from the transom to drop the engine to the right height.
Depending on the hull design that could cause problems.

Yep , not an option
 Chopping back a transom.. well ok going back to the old school short transoms if just potter around in a quiet bay.. any more than that  and the risk of a wave into the boat over the stern, sudden weight , down she goes by the stern..
Not uncommon with inexperienced skippers in old hulls ..cruise along, stop sudden, or hull turns into the chop from the stern when pulling anchor.
 
Adding a pod on the back should make it possible, but that's a

 Also adding pods on a hull and layout, that is not designed to to carry that extra weight and the leverage of that weight, out on a pod has a negative effect on the hull performance..

This is where thinking the current 20"  goes on a more modern boat with a pod, as in a Ramco for example..
 The 25" gose on the 20" transom with height increased..
Rebuild or  plate or even a  2" jack plate .. all easy 'fixes'

lot of work compared to just buying a boat with the right OB and selling your current boat as is.

 this is where things are not working out well...been watching for around a yr now, some well priced and suitable hulls, but tend to be under powered for save bars crossings if things go wrong... even on granny crossing days.
 But swap outboards leaving the current over powered , well powered and the new hull well powered for bars and west coast .
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There you go "steps" sorted

https://www.trademe.co.nz/a/motors/boats-marine/motorboats/listing/3056515681?bof=Wuef94xS

 Thanks but already on the watch list, and an example of why this thread , as explained in post above.

Have googled ramco 6m and all have 115hp  must be a reason

We are looking not only at Ramcos , mclays, several makes . glass and alloy..
 Do your home work on the hull weights , estimated gross weights on the water, manufacture spec, engine powered specs, older reviews and some things become very obvious very quickly.
 1/ 115 is towards the mid to bottom end of power specs
2/ Reviews on hull performances with basic unloaded boats with these lower than max manufactures recommendations, give reasonable results.. till they are loaded up with gear , 100 odd L fuel, 3 or 4 good sided guys.. And then the performance will drop.. dramatically below that for heavy sea/ bars etc.
3/ Many boats a re brought on budget, which means 'like the big hull'   and dont like the big tag on the most suitable powered engine for the hull... and in near all cases , the engine gets hit with the budget... cause the sales person doesnt tell them about this stuff..

And then I get asked (so bloody many times ), what can I do to the prop to get my boat to perform like the demo boat? 
Its not a prop issue its a power/ weight  issue...you are carrying an extra 200 kg plus than the demo boat.

So we are stuck in the 2nd hand boat market with so many min and ave powered hulls...

So the question

must be a reason?

 thats why.. covered many times in these forums over the last yrs..
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Post Options Post Options   Likes (1) Likes(1)   Quote MATTOO Quote  Post ReplyReply Direct Link To This Post Posted: 10 Sep 2021 at 5:09pm
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Hi Steps,

Well I could be wrong.
But my understanding on the establishment of long legs came about based on three learned experiences from manufacturers.

Smaller outboards progressed there lengths based on yachts that required an ability to have a small outboard lowered on a transom lower attachment that accommodated for yachts high freeboard.

The second consideration was based on the American market for engines approx 90 up and above that could fit developing hull shapes from bass boats to offshore users.

The third and probably the most import was for engines say from 90 hp and above that were proving inherently unreliable in water states salt or fresh.
The principle problem was water through the air filter.
It relates to the high atomisation of water particles behind the engine that were drafted back in to the air intake.
As a result of complimentary solutions raising the height of the motor was one of the used options in conjunction with repositioning the air intakes, filter positing and laddering of air intake.
That's a simplisticc overview but outlines the principles as I understand them.

So when putting an engine of any leg length the principles your aiming for are the cavitation plate being within an adjustable length for prop performance.

The capacity or displacement of the rear of the hull due to regular weight capacities of the hull.

And the ability to have the engine at the highest achievable position relevant to its air intake and sitting position at rest.

Hope that helps.
Just cruising in my now sweetas pimped out Southern 755 HT0!
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 10 Sep 2021 at 5:40pm
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Thats all  helpful to very helpful.. the history sorta had a very abstract knowledge on it.. Espec about moving from fresh water to open .
 Even to this day their river boats have very short legs.. propping a couple atm ...and happened to ask about this.. totally un related thu.

It relates to the high atomisation of water particles behind the engine that were drafted back in to the air intake.

 This .. I have mentioned many times about things like transducer putting up spray around transom mounted engines, and talk to work shop guys.. a common issue for slow death to an engine. Hence why I have built a cover spray over my transducer.

 And thanks for the reminder, havnt even given that a thought.

 
Just thinking thru here, and comments if got right or not.
OK a Ramco , general  pod type hull... transducer is well back  plus on hulls designed with stringers etc in mind for transducers etc..so not low like my current low one, because did not exist back then..
Other stuff that send up sea spray around the engine with engine back on a pod..
I notice (get impression only) that the spray tends to come off the bottom of the hull, and other places, then gets sucked back into and often over the transom into the boat, rather than sent back out over the engine cowl..
 Cant think of any other parameters..
 So it would follow (???) puttting an engine out on a pod ,espec if there is a duckboad around it , and still a 20 "

 Would be more of an advantage???

 Thu no duckboard, a transducer cover could still be required anyway???


And the ability to have the engine at the highest achievable position relevant to its air intake and sitting position at rest.

That also passes through my mind abstractly when out.. just how low the engine cowl appears on the back .. regardless if a V4 or V6.. the extra weight made little difference...
 Thu at rest, most of the time the hull points into the wind, chop, and sheltered.. Its more a splash from a shark attacking it rather than fine  sea spray... and its not running to suck that moisture into the intakes.

 yeah points that need a little more thought..
 Thanks.




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PS gone back to the link PJc put up .. Has a very good shot of the pod...
 messing with a few sketches..
 If one puts 2" a jack plate for a 25" on a 20" then it is NOT 5" increase up its about 5 1/2 to near 6" higher.. due to
1/ The elliptical  curve of water surface further back from the transom ,
 2/must take into account the 12 deg (most common ) angle of the transom.

 So if reducing then it may not need a 5" chop...(???)

And looking at the Ramco set up there could be enough 'room' to do the chop with little complication... if any.

Trouble is getting good pics of the boat for sale to see.. and lock down.. stuck at home , yards etc also closed..
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Post Options Post Options   Likes (0) Likes(0)   Quote krow Quote  Post ReplyReply Direct Link To This Post Posted: 10 Sep 2021 at 8:57pm
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I can take some photos of mine if you like. Ramco fishmaster 6m with 135 (not 115) 
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135  that will make the mass (weight ) of a 6m ramco handle nice .. What is your WoT , normal load on flat water? getting up into the mid to high 40s mph ?.. at least?

The pics on the link above are pretty good, couple more closer up would be nice, see how constructed with thoughts to modding.
 Also a few measurements.
 Most hulls have a at rest water mark on the stern...
1/the distance from that to top of the pod?
2/distance to the center of the top mounting bolt.?
3/ Which  of the mounting hole is being used?
4/ your comments on the viability as to strength, etc to modding the pod down 5"  and 6"

 Cheers for that.
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Mattoo Krow and who ever else..

Mattoo
 Above I sort of passed over your comments on water height, exhaust etc.. but did slip them into my brain..
Im playing with limited data/ measurements.. which made me go back to your post for reference.

It seems, I dont actually know, the more modern boats , as you sort of referred to, have a greater distance from the water line at rest than the older flat bottom/ gull wing type hulls.
If so or those that do have greater distance then a 20" becomes problematic..as you mentioned..
 I think i now understand what you actually meant.

The distance from the keel to water level at rest is 12" on the V6 over powered 150 20" on the back of our gullwing transom.
The distance from keel to exhaust is nearly 23"
Which puts the exhaust 10" above the water level at rest.

Which if that 12 " increases eg because of a deeper V at the stern the exhaust gets closer to the water surface at rest..

So Mattoo Krow others , yes would like some measurements on around 6 m  Ramco, mclay, fryran buccaneer 605, marco quintrex, haines.... etc hulls.
 These and others are all on the possible list to buy... and looking for measurements on them

 Essentially, looking to buy in these parameters.
 around 6m..
Alloy or glass.. alloy post around 2001 (thicker hull panels)
Cabin, cuddly of some sort.. with Ht or bimni (latter can get made)
Winch or capstan
Reasonable engine hrs, 2S or 4S, well or over powered for gross weight, generally around 45 mph+ WoT.

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Post Options Post Options   Likes (0) Likes(0)   Quote krow Quote  Post ReplyReply Direct Link To This Post Posted: 11 Sep 2021 at 5:50pm
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Rest water level (about) 250mm to top of pod but pod is on an angle down to the motor mount so a bit less at the mounting face. 
top at the face to the centre of the top bolt 55mm
Centre of 5 mounting holes (see pic).
My pod must be a bit low as there is a 40mm gap between the top of the pod and the  engine. Another photo attached.



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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 12 Sep 2021 at 9:09am
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My pod must be a bit low as there is a 40mm gap between the top of the pod and the  engine.

That approx measurement  is pretty std on a general use hull. If go from east coast to west coast and East coast is set close to the  top height limit... then one finds they drop down a hole.
And when setting for more barge type use allows to set down lower.
 Racing.. well really high.

top of pod but pod is on an angle down to the motor mount

 Thats pretty much a std 12 deg angle on most planing hulls.. pod or transom. I think I mentioned above about if increasing a transom /pod from 20 to 25" one has to take into account that angle.

top at the face to the centre of the top bolt 55mm
Centre
 Factory install manuals say this distance should be a minimum of 1 1/2"   (about 38 mm) just make sure talking same .. top mounting bolt center to the top of transom/ pod

What is the distance from water level at rest to the exhaust port just below the cowl?
 Distance from cavitation plate (25" leg) to exhaust port?
 And vertical distance from keel to top of the pod?

 Think that enough to work out the rest of the distances (?)
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Post Options Post Options   Likes (1) Likes(1)   Quote Big -Dave Quote  Post ReplyReply Direct Link To This Post Posted: 12 Sep 2021 at 12:32pm
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Ok, I've read through the comments..
Some thoughts..
It makes sense that as boats have become deeper in the vee, that outboards would need to sit lower, so longer shafts to keep the power heads clear make sense.

Before I chopped the transom off on my new project, I researched the standard transom heights. Seemed to keep coming back to 6235 mm which is 25 inches. Now the transom I just took off, I had at 680, and the motor sat quite high off that. Had approx 12 degrees on the plate and if you extended that angle it was very close to the vee of the hull at the bottom.
This all put me in a mind spin as to what I should do, don't want to chop a transom too low only to need to raise it again.
Asked my son who fits motors, their jig sits on top of a transom, no reference to the bottom of the boat, this top edge is determined by the manufacturer, the further back off the hull, the higher it must get.

In the end, I wheeled the motor out(I made a stand with wheels), parked it up against the boat and yep, it seemed with the motor at 90 deg to the hull line, 635 was correct. I chopped it there.
Yet to fit and try it out.

So, Steps, if a boat has a pod, I'd assume it is already raised to allow for the elliptical curve of the water coming off the hull, and a 20 inch shaft will still be too short. Look at the height the current motor is at, yes you might be able to put your 20 inch on 2 inches lower without chopping, but that might not be enough. Some props seem to cope with ventilation better than others, think surface piercing..that might work..
All in all, I think you are better to stick with a 25 inch motor on a 25 inch designed boat. Keep an eye open for a dead donor motor for a 25 inch leg..?

My son recently picked up a 90hp yammy, when we looked, it had a 25 inch leg, spacer type..not the 20 advertised. But we thought hey, we can stick 5 inches on, he's a boat builder...turns out his boat had a 16 inch transom...damn...we have found a dead 20 inch 90hp, are negotiating acquiring it as the rest of the existing one is serviceable.
you can't fix an idiot with duct tape, but it does muffle them for a while...
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 12 Sep 2021 at 5:39pm
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yes
 I think that deeper V.. distance from the hull keel line being greater on modern boats , allowing for the elliptical curve.. even thu further out on a pod  is a plus, to the height of the  top mounting bolt, which should be at least 1 1/2" from the top of the pod/ transom.
 The 12 deg pod transom makes a surprisingly big difference in heights as against straight vertical height..

 A few more numbers to play with and scaled sketches.
 Damn its hard to find good old fashioned graph paper these days...
 May turn out as you say..being you most properly will Wink
Some thing I just have a need to find out for real myself.. just takes bit help .
 Thanks for that m8
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