20" on 25" transom?

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Post Options Post Options   Likes (0) Likes(0)   Quote Big -Dave Quote  Post ReplyReply Direct Link To This Post Posted: 12 Sep 2021 at 8:17pm
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I brought an exercise book of graph paper...the warehouse.
Yes, with a 12 degree transom, it's surprising how far back the motor is when at 90 deg to the keel line.
I've a feeling my motor might end up on the bottom hole..
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 krow Quote  Post ReplyReply Direct Link To This Post Posted: 12 Sep 2021 at 8:50pm
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Not quite sure about the exhaust port near the cowling as the only exhaust I have is out the back of the prop. Distance from cowling to cavitation plate is 700.
Bottom of v to top of pod 520.
Yes 55mm from centre of top bolt to the corner of the aluminium pod. 
BTW I think my pod might be more than 12 degree as I had to install a wedge between the pod and the motor to get enough trim. You might be able to see it in the photo. 

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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 13 Sep 2021 at 11:15am
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Not quite sure about the exhaust port near the cowling as the only exhaust I have is out the back of the prop
 Different brands, 2S 4S yep. distance from bottom of  cowl will give me a good ball park Thumbs Up

I think my pod might be more than 12 degree as I had to install a wedge between the pod and the motor to get enough trim. You might be able to see it in the photo


Yes saw the wedge, wasnt sure if was a wedge or the insulation pad.
 Even if the std 12 deg, sometimes the engine needs a wedge because of the balance of the hull.. where stuff stowed usually.. or can be a prop with incorrect rake.. or can be 'fixed by changing to a prop with different rake.
 They all work just as well as each other.

Yes, with a 12 degree transom, it's surprising how far back the motor is when at 90 deg to the keel line.
I've a feeling my motor might end up on the bottom hole..

Tagit, damn miss his info.. put me onto that when I was looking at 20" 25" jack plates way back... I had decided if was going to put a 25" on a 20" transom  making up my own alloy channel jack plate was very high on the list..
 He said the difference between the engine being vertical at cruise and the difference between the 20 and 25"  12 deg transom length is far greater than one would expect.. then add the extra distance from the transom of the jack plate...
So I did the maths, including measuring the elliptical curve off the keel at several distance back from the keel at cruise (35 mph)
 Its my understanding this is rather a common install error even in  professional/ experienced work shops..
\
Dave:
Graph paper sorted for now... download pdf s and join the A4 printouts together.  Checked out on line, warehouse stationary have graph paper books as you say.
Looking for those big sheet pads of graph paper used to buy about 500mm by 750 mm (?)
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Post Options Post Options   Likes (0) Likes(0)   Quote MATTOO Quote  Post ReplyReply Direct Link To This Post Posted: 13 Sep 2021 at 5:27pm
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Some things I see in posts that haven't been raised that might fill in a few holes or conversely create more questions.

Many modern motors have substantial trim formats.
The installers generally know them but your manual should have them.
They can set base and maximum range formulas.
They make considerable handling differences.

Another thing is the drain holes of the head covers and base area of there mounting and cavity of there construction that can store water.
They all have them and some manufacturers denote them as points of reference to be above a waterline
position they determine.

If a mono hull, stick with a cavitation plate that can be adjusted with in one inch of the lowest stern point of the mono hull.
Just cruising in my now sweetas pimped out Southern 755 HT0!
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Post Options Post Options   Likes (0) Likes(0)   Quote Dan12ft Quote  Post ReplyReply Direct Link To This Post Posted: 20 Sep 2021 at 1:53pm
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Sorry for hijacking your post,
I have a 13.5ft alli-craft with a 15inch transom. Im wanting to raise it to 20inch so I can fit a 30hp outboard (hull is rated to 25hp) as I would like some more free board. Its hard to find 25 or 30hp outboards in a 15inch shaft also, any help or ideas on how to do it properly. I dont have a welder so im thinking of getting it professionally done but a diy version would be great also. Cheers Dan
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Post Options Post Options   Likes (0) Likes(0)   Quote Big -Dave Quote  Post ReplyReply Direct Link To This Post Posted: 20 Sep 2021 at 2:09pm
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Originally posted by Dan12ft Dan12ft wrote:

Sorry for hijacking your post,
I have a 13.5ft alli-craft with a 15inch transom. Im wanting to raise it to 20inch so I can fit a 30hp outboard (hull is rated to 25hp) as I would like some more free board. Its hard to find 25 or 30hp outboards in a 15inch shaft also, any help or ideas on how to do it properly. I dont have a welder so im thinking of getting it professionally done but a diy version would be great also. Cheers Dan

Anything DIY will be a bit dodgy unless you have a welder and good materials, Id be finding a local shop and getting a price.
16 inch motors are next to impossible to find.

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: 21 Sep 2021 at 10:15am
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Is this a glass or alloy hull?
 Glass can be simply done with a alloy plate bolted to the transom over the section of engine well. Being smaller weight power, a wood 'plate' cut to fit in the old engine bay, behind the plate, then braced (bolted tru the transom ) support each side of the well.

I would imagine an alloy hull could be done the same way.

Pretty much a saw , drill files, maybe 4" grinder/ cut off blade.



Or along these lines with a fitted section board to increase the well height.


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Post Options Post Options   Likes (0) Likes(0)   Quote Dan12ft Quote  Post ReplyReply Direct Link To This Post Posted: 21 Sep 2021 at 11:59am
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Thanks for your reply big-dave and steps, I should have said I am a qualified builder so i have general tools witch im very familiar with. im just not sure if im over thinking it as im a coastguard volunteer so I see some actually dodgy stuff. I am thinking of using marine hardwood ply and laminating it together, then coating it in an 2part epoxy sealer with 10×100mm aluminum strips either side. Of the transom to stiffen it. I was also going to hard pack it with 2mm packers and marine ms silicon to make a barrier between the aluminum. I have been thinking about buying a jacking plate but that moves the weight further back, slightly yes but it will apply more leverage on the transom.
Im trying to upload a picture but it won't let me, the boat is a 90's aluminum boat witch is welded and rivet, its simular to a 13ft fyran
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Post Options Post Options   Likes (0) Likes(0)   Quote Big -Dave Quote  Post ReplyReply Direct Link To This Post Posted: 21 Sep 2021 at 12:56pm
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That sounds like a reasonable way of doing it Dan, and you are not trying to support huge hp or weight.
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: 21 Sep 2021 at 5:36pm
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Im with Dave .. maybe bit of over kill thu...
Only thing would consider the extra weight on transom at anchor on a small boat. ???
Maybe work out the weight.. launch in the bath tub  (lockdown restricts anything more...and see how sits ...
 Seriously thu.. load the weight in the stern , and float it off the trailer..


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Post Options Post Options   Likes (0) Likes(0)   Quote Dan12ft Quote  Post ReplyReply Direct Link To This Post Posted: 21 Sep 2021 at 6:58pm
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I would agree it is probably abit overkill, would it just be better/lighter to get some 100×50 6mm or 120×50 6mm aluminum tube (even 4mm would work) and bolt through the transom cap. I know how the boat sits at rest with a 15hp and 3hp auxiliary on the stern with 10ish kg of gear and its okay but I would like the extra 100mm. The tohatsu 30hp longshaft is 51kg and my yamaha 15hp is 36kg with a 12kg auxiliary next to it. I think im just overthinking it as i fish the west coast (kaipara and manakau) so I know the swells can cut up, I have been fishing there since I was born so very familiar with it.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 22 Sep 2021 at 9:00am
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buying a jacking plate but that moves the weight further back,

 So was I then came across the above pic.. keep as close to the transom as possble back would be significant. Ullrich Aluminium in Wiri
Simplest soln and uses the orginal transom mount holes.
 Then your board(s) or another alloy plate to increase the height of the transom, cut to fit. Maybe also bolted to the Alloy channel.
 An alloy box section across the back of the insert and transom just to add a bit of over kill... or alloy channel or angle to cap the top of the tramsom.

Yeah when I was looking around saw some rather dodgy set ups.. the thing is, when got close up, most where good in principle just way under built or secured for my liking.

Keep it simple thu..
Yes laminiate marine ply as you say, seal with a good 2 pot method.. no need go over board thu...
 In practice lets say you used std ply .. the better grade for structure..laminate and seal edges with the 'glue'  That will last for yrs. It gets wet, and dries.
 Issues with wood transoms is because they are below water line... even those couple inches is a lot pressure forcing any water into that timber if a leak... then throw in, are sealed and dont get to dry out...
Top of the transom, not under pressure, its surface 'spray, and dries out.. even on the water on a nice day.

I changed my under floor tank to 150L.. couple mm higher for had to make a floor 'plate to cover'  At the time had a sheet of that elcheapo ply, so what the hell no biggie to replace in the future... 4 coats polyurethane, lot use, gets regularly hosed, and waterblasted... After few yrs had to lift it to clean bulges other week... still 'new' solid as... oh and gets rained on one end and sits up on wet carpet each side.
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