Aerotec transom splash issue.

[Locozodiac]

As boats are not cars, buses or motorcycle in which you do nothing on them right after your acquisition, read the following information as to understand provided tech concepts.

General tech information to consider, has been confronted and deeply water tested over and over till satiety with excellent results :

-All motor brands have slight length differences in between upper and lower plates doesn't matter if being S or L sizes.

-Each motor installation is unique, if height seated to perform good, not top though will need to make a new installation when passing to other motor brand and sometimes when going for 2 different HP motors while maintaining same brand.

-When testing to find the sweet motor/transom height spot must be done on flat calm water cond, with deck weight evenly distributed and motor trimmed to 90 deg. Did you know that a motor wrongly height seated along badly trimmed leads to awful water performance and frustration as in examples. ( Pic 1)

-Going per the idiotic rule of thumb that states that lower plate must be even, near even with middle aft hull is a tech fallacy, no one has consider that each boats floats more or less according to their hull shape and their own floating coefficient. All boats have been thrown in same sack which is ain't so.

-Float 3 different same length brand boats along 3-15 HP different brand motors, all 3 will perform different from each other when water flow exits right through middle aft hull onto lower leg. One of them might work OK, the other will achieve back, side or even over transom water splashes, the third one will achieve light to severe prop aeration. As this is pure theoretical speculation, under practice any of them will achieve one of the stated working conditions.

-Short shaft transoms ranges from 37 to 40 cm, long shaft transoms ranges 50 to 53 cm. Same with motors, Yams are slight less larger than Tohatsu which are 2 of the motor brands I most install.

What it’s important to determine in each own's particular case is : which is the ideal lower leg height for spot on water performance, on calm flat and rugged water conditions, top maneuverability and seaworthiness.

Question :

If you could instantly modify the transom height, which of the 3 lower leg heights (pic 2) would you choose for top boating, what kind of water performance would you expect to achieve with the chosen one ? Be welcomed if anyone would like to chime in and post their own ideas on the subject.

Already know the answer for each one as have tested all 3 heights in same boat myself at a rowing court facility (pic 3) Just wanted to know how boaters addresses what’s going on at back transom when motor is at full wot operation.

Happy Boating

[Fenlander]

Locozodiac this has been a great thread with loads of advice for Aerotec users, the Aerotec having a very specific water flow and splash issue not easily understood unless you've used one.

Five years ago you started a couple of threads with the same content and questions as your post above which ended up with over 100 posts between them...and you referring to those that didn't agree as... Lazy, stubbon, wasting your time, posting nonsense.

Please don't dilute this Aerotec thread in that way. Here is your thread...

http://www.rib.net/forum/f50/lower-u...tml#post796626

Regarding using a Tohatsu 18 2-stroke on an Aerotec I have no idea of how that might splash but DanExe has just bought one for his Aerotec so we might find out soon. I like that motor, was offered one this week and did consider it but they are too heavy for me.

[smallribber]

Originally Posted by Fenlander

Yep seems so. Too complicated to explain on this thread but needs, wishes and aspirations have aligned to pull us back to a post 2000 15hp 2-stroke. A potential buy is on the cards and if it works out I'll chuck a post up.

Heck

Just after I listened to all you chaps about 4 stroke and bought one you are going back to 2 strokes.... Still no matter I keep mine so now have
9.8 HP Tohat 2 stroke
15 HP Merc 2 stroke

20 HP Merc 4 stroke


All have their uses and I am soon to try my vintage Seagull 2.5 hp

[smallribber]

Originally Posted by 69cmw

Attachment 129681

Like this [emoji41]

I got one of them and love it

[Fenlander]

BP it's simply all about the weight for me as for the foreseeable future we will be carrying the sib in the car daily inflating on days out.

When I bought the new 9.9 4-stroke last year I knew... and so it proved... it would be acceptable for performance on the Aerotec but we also had plans to downshift the sib soon and restrict ourselves to mainly estuary pottering hence the 9.9 would be ideal.

However various factors have made us realise there are such minimal weight savings (re handling ashore) when dropping to a smaller sib (as the Aerotec is so light anyway) we will keep the Aerotec for some years. And as my comfortable OB weight for lifting is close to 36kg it leaves but one option.

As I said above full circle!

[Glow]

I have a 20hp 4 stroke and I too am considering downscaling to a 2 stroke, ideally an 18hp but every one I have found lately has been a dog.

I actually bought one from a local dealer, the cooling system was completely blocked solid and so I returned it immediately.

The 20 is quiet, smooth but super heavy, it makes moving and handling stressful, not a good compromise.

[smallribber]

Originally Posted by Fenlander

BP it's simply all about the weight for me as for the foreseeable future we will be carrying the sib in the car daily inflating on days out.

When I bought the new 9.9 4-stroke last year I knew... and so it proved... it would be acceptable for performance on the Aerotec but we also had plans to downshift the sib soon and restrict ourselves to mainly estuary pottering hence the 9.9 would be ideal.

However various factors have made us realise there are such minimal weight savings (re handling ashore) when dropping to a smaller sib (as the Aerotec is so light anyway) we will keep the Aerotec for some years. And as my comfortable OB weight for lifting is close to 36kg it leaves but one option.

As I said above full circle!

There is a nice one on Gumtree at the moment. for a good price

[Fenlander]

A Mercury 15? Can't see it.

[Stevem]

For info. Tohatsu mfs20e with no riser shim. About 18 knots in the video, very limited splashing.

https://www.youtube.com/watch?v=AhGcPInoLPk

[Fenlander]

That looks good Steve... and smooth sounding too.

[smallribber]

Originally Posted by Fenlander

A Mercury 15? Can't see it.

https://www.gumtree.com/p/boats-kaya...at-/1341838100

Click through this add... It is a Mariner but same thing

[smallribber]

So many people shoot videos with their phone the wrong way round... They should be held landscape as you cant rotate videos

[Fenlander]

Actually a very good possibility and thanks for the link BP but the round tiller model with blue coils is a little too old for me.

Having said that had it been local I'd have been round for a look like a shot.

[Max...]

Sweet spot always has been 3.4 to 3.8m airfloor SIB + 15 hp 2 stroke. *The* compromise outfit.

[Locozodiac]

What posted was the whole pack of ideas including clearing misconceptions going around for years now that needed to be known about.

This Aerotec thread seems will continue forever if not put to and end under water trial and error. Steven has posted a video, would like to ask what do you mean when stating there was a "very limited splashing" going on. To me a video shot at transom's front doesn't say much at all when looking backwards.

Ideal would be to know if the splash is being produced by the altered water flowing out middle hull due to rear lower non stretched fabric issues or if the altered water flow is banging higher than the non edge portion located between upper and lower plates.

Poster stated no transom riser being used, be aware that riding with both transport wheels attached at back transom will exert more weight on transom and consequently lower leg will ride more deeper than without the transport wheels attached.

Is it possible to post 2 new video shot over the transom, say motor side with wheels and without them to really know what's going on at back of motor. If you haven't visually check it as suggested will be a wild guess guessing where is that back splash spot being produced.

Happy Boating

[SixtyNorth]

Don't you have a RIB now?

[jeffstevens763@g]

Loco you seem to be getting very technical with this the aero tech owners no full well what the issue is some engines fair better than others for the splash over the stern. In contrast to the problem of the areo tech my boat doesn't suffer any of this at any speed or loading but one day I had an excessive amount of water coming over the stern it turned out to be a small piece of paper trapped in the Eddie created by the hull right next to the transom so it doesn't take much to cause the same scenario.

[Fenlander]

I did comment on this in the engine thread but perhaps useful to add to the Aerotec splash vs OB type data.

Once I'd sorted the trim pin position and distribution of fuel tank and heavy anchor bag etc... with the 45mm transom lift mod I already had... the Yamaha 15 2-stroke performs well on the Aerotec. Given the slightly over-pitch prop which I'll change soon the speed is good and tight turns are excellent with no ventilation. Similarly no ventilation when driving into a difficult sea. The wake is untidy with the usual central splash that falls behind but no problem with water over the transom and only the odd spots being thrown onto the outboard hood.

It may be fine with a lower lift than 45mm but there's no reason to undo my work as the only reason I'd have for that is if there had been ventilation on turns.

I'll just try it with whatever new prop I buy to make sure that doesn't ventilate either then I'll drill the OB bolt on holes... and perhaps I'll have a setup that can remain for a few years with no fiddling.

Image below was with OB trim in wrong posn… even less splash with that corrected.

[Locozodiac]

Originally Posted by jeffstevens763@g

Loco you seem to be getting very technical with this the aero tech owners no full well what the issue is some engines fair better than others for the splash over the stern scenario.

Yes, if wanting Boating Perfection need to be very technical when installing motors. No S or L motor brand will perform exact same while sitting on same boat's transom due to slight lower leg lenghts differences between them.

Ideal is to install them at a certain height to achieve top prop thrust, spot on water performance on flat calm and rough water condition and impeccable close tight turns at speed with no prop aeration. Only achievable through lots of trial and error water tests.

Happy Boating

[jeffstevens763@g]

you need to read the thread in more detail do you think that a guy would go to all the trouble of glueing pieces on his hull if he hadn't explored every other avenue and that his research into hull design and the characteristics that cause the turbulence and splash issue lead him to redesign the original boat.

there was a hook at the transom caused by the intersection of the floor to transom which any amount of engine position wouldn't stop the turbulence/splash in most cases, but some engine legs are better that others & some lifting their engine gave them acceptable splash to them or purely making a splash plate for others was enough for some who want perfection go the extra mile.