Advise for buildin aluminium hull.

Airboats with smaller powerplants.
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M0RYAK
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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Wed Oct 30, 2019 12:09 pm

Need help! I have the big problem with dolphin effect.

Should I rise or down aft part of moto frame?

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Re: Advise for buildin aluminium hull.

Post by Gary S » Thu Oct 31, 2019 6:30 am

You would lower the back, just like outboard.

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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Mon Nov 04, 2019 1:59 pm

The rear of the engine lowered, but dolphin effect keeping, after 30 mph. Remark, the prop lower behind the transom about 8". I think it may be reason too, because transom and flatbottom have angle more then 90.
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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Mon Nov 04, 2019 2:37 pm

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Slidin Gator
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Re: Advise for buildin aluminium hull.

Post by Slidin Gator » Thu Nov 07, 2019 8:31 pm

Moryak,
Watched the video, she seems to have good power! I like the sound for sure :cheers:

The start of the video shows the boat floating without power and she is sitting nose down, A LOT. Then when under power she rides nose high, like she should.

Given that you have a rather light engine and gear setup, I think you have too much nose weight and need to move some weight to stern. It might be that fat ass guy on the pillow, :slap: but you are probably always gonna have to drag some fat guy around :angry5:

I think you have too much nose weight and at present the prop is angled too high to compensate. Move weight aft, the result will be a higher nose at idle and more porpoising at cruise. Then you can trim the prop/engine down to ride level and settle out the porpoising.

Keep in mind that your design includes one key difference from most of our boats. Your boat is not flat at the nose, you held the chines all the way to the bow. This decreases your flotation on the nose. Combine that with less engine weight and your boat needs weight in the stern vs. the nose.
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Re: Advise for buildin aluminium hull.

Post by SWAMPHUNTER45 » Thu Nov 07, 2019 8:42 pm

Cool video, make sure your buddy takes the shells out if your gonna spin that rascal...lol

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M0RYAK
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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Tue Nov 12, 2019 11:09 am

SWAMPHUNTER45 wrote:
Thu Nov 07, 2019 8:42 pm
Cool video, make sure your buddy takes the shells out if your gonna spin that rascal...lol
Thanks! It was done.

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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Tue Nov 12, 2019 12:28 pm

Slidin Gator wrote:
Thu Nov 07, 2019 8:31 pm
Moryak,
Watched the video, she seems to have good power! I like the sound for sure :cheers:

The start of the video shows the boat floating without power and she is sitting nose down, A LOT. Then when under power she rides nose high, like she should.

Given that you have a rather light engine and gear setup, I think you have too much nose weight and need to move some weight to stern. It might be that fat ass guy on the pillow, :slap: but you are probably always gonna have to drag some fat guy around :angry5:

I think you have too much nose weight and at present the prop is angled too high to compensate. Move weight aft, the result will be a higher nose at idle and more porpoising at cruise. Then you can trim the prop/engine down to ride level and settle out the porpoising.

Keep in mind that your design includes one key difference from most of our boats. Your boat is not flat at the nose, you held the chines all the way to the bow. This decreases your flotation on the nose. Combine that with less engine weight and your boat needs weight in the stern vs. the nose.
Ok! Good remarks, I think the same too. But, I tryed move all weight to stern (two men plus 80 lbs equipment), don't possitive effect, I was continuies push acelerator after beginin dolphine effect, my boat start fly. I tryed run without bow guard (nose), no possitive effect.

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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Tue Nov 12, 2019 1:08 pm

Guys. Note my airboat design have difference high of boardside. She has 60 cm at stern part and 50 cm bow roll. It's reason of visual effects.
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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Tue Nov 12, 2019 1:18 pm

I was little bit cut the transom.
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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Tue Nov 12, 2019 1:40 pm

I am very happy. It's my first experience. For mi very important stability and maneuvering, but I want increase the speed to 40 mph. Now I restricted by sufficient place for mowing the prop. I want try use the transome plate.

P.S. it's boat no fuel economy.
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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Tue Nov 12, 2019 2:39 pm

Additional! Guys, I have possible use some gears ratio, it's cool. I tuned prop for first gear 11000 rpm max at engine (2683 rpm at prop). And I have 7700 rpm at engine max for second gear (2265 rpm at prop). And I tryed use the third gear it possible without passangers on shallow water, 5000rpm max at engine (2000 rpm atprop). Optimal second gear (dry run possible without passengers). With the first gear it is rocket.

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M0RYAK
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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Tue Nov 12, 2019 4:11 pm


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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Wed Nov 13, 2019 3:04 am

What approximate angle between prop and bottom? Now I have 90 degree. What limits possible?

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Re: Advise for buildin aluminium hull.

Post by SWAMPHUNTER45 » Wed Nov 13, 2019 7:45 am

Looking at the video with your friend in the boat tells me it is a weight and balance matter. Smaller boats can only carry so much weight and it is doubtful you can tune that out.

With engine prop angle we will use stainless fender washers and slowly add them testing the change it creates.

All in all the boat you built is very nice and is performing fairly well all things considered. I was unable to really see a clear shot of the boat running straight at speed to offer an opinion of it's driver only running balance.

I would play on the side of caution when you get into a little deeper water because dipping a corner will cause you to flood the hull in a near instant. This would be most likely when making tight turns or if the stream is narrow and you get a wake coming back at you.

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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Wed Nov 13, 2019 11:00 am

SWAMPHUNTER45 wrote:
Wed Nov 13, 2019 7:45 am

With engine prop angle we will use stainless fender washers and slowly add them testing the change it creates.

All in all the boat you built is very nice and is performing fairly well all things considered. I was unable to really see a clear shot of the boat running straight at speed to offer an opinion of it's driver only running balance.

I would play on the side of caution when you get into a little deeper water because dipping a corner will cause you to flood the hull in a near instant. This would be most likely when making tight turns or if the stream is narrow and you get a wake coming back at you.
I have the same possibility. During first run I used 11 stainless fender 2 mm each at stern part of frame. I removed the all stainless fender and don't found changes with run. Before second voyage I drill new rings for aft silentblocks of frame and lower the aft part 20 mm. Don't found changes. During third voyage I drilled the new rings for ahead part of frame and rised it 10 mm. I don't found possitive effect from thise operations. All time I lowered aft of engine (55 mm summary).

Thanks for warning!

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Re: Advise for buildin aluminium hull.

Post by SWAMPHUNTER45 » Wed Nov 13, 2019 2:07 pm

i would say keep the engine level and consider a slight shift of weight rearward. That said your nose heavy condition with a passanger may just be a limitation of your boats size.

Enjoy the new boat and ride safe

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Re: Advise for buildin aluminium hull.

Post by Slidin Gator » Wed Nov 13, 2019 7:05 pm

Swamp, Moryak is trying to solve a porpoising problem. It sounds like he started with 22 mm, about 1” of shims under the rear.

#2 he removed those shims and porpoising remains.

#3, dropped the rear of motor frame an additional 20 mm, 3/4” and the porpoising remains.

That is an awe full lot of adjustment with no change!

Moryak,
Are you sure the bottom is flat? This sounds more like a hull tuning issue vs. prop angle.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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Re: Advise for buildin aluminium hull.

Post by SWAMPHUNTER45 » Wed Nov 13, 2019 7:47 pm

Yea my bad Chuck I thought he was trying to get it off its nose.

It rides nose down with a passanger and hops when he rides solo ?

If he puts a hull jack in the rear its only going to make his problem when loaded worse. This may be the time when a trim tab is the best remedy

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Re: Advise for buildin aluminium hull.

Post by M0RYAK » Thu Nov 14, 2019 10:00 am

Slidin Gator wrote:
Wed Nov 13, 2019 7:05 pm
Swamp, Moryak is trying to solve a porpoising problem. It sounds like he started with 22 mm, about 1” of shims under the rear.

#2 he removed those shims and porpoising remains.

#3, dropped the rear of motor frame an additional 20 mm, 3/4” and the porpoising remains.

That is an awe full lot of adjustment with no change!

Moryak,
Are you sure the bottom is flat? This sounds more like a hull tuning issue vs. prop angle.
Yes! Bottom is flat.

During first time I used airboat with empty fuel tank and at deep water. I want try again it but at shallow water and try rise the aft part of engine and load aft part of hull.

I try create more video and photo for understanding.

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