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31 May 2020, 17:25
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#1
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Member
Country: UK - England
Town: teesside
Boat name: magic
Make: humber 5.5
Length: 5m +
Engine: mariner 115
MMSI: 232012453
Join Date: Apr 2014
Posts: 1,558
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A little advice please
anyone any ideas on this problem took my boat out today to put a few hours bedding the new outboard in .its a humber destroyer 5.5 with new mariner 115 command thrust mounted second hole from the top .the av plate is roughly 2 inch above the keel line . in the water planing at 16 knots the av plate looked to be just above the water . fully trimmed down . now when i upped it to 4k rpm about 25 knots and tried to trim out it started to lose grip and cavitated revs were up and down to 5.5k rpm with no increase in speed trimed back in and it gripped again . bear with me I am not sure on the size of prop supplied with the outboard ( its a new outboard new prop and i cant check as i left it on a mooring for tonight ) except its a 17p but on the invoice it says supplied with a 19p prop . could this be just too small a pitch prop or is it more likely to need the outboard dropping a hole. thanks
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31 May 2020, 17:41
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#2
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Member
Country: UK - Scotland
Town: Easdale
Boat name: Miss Isle
Make: Solent 6.9
Length: 6m +
Engine: 225 optimax
Join Date: Jan 2008
Posts: 1,427
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For straight line economy/speed trim out until you lose grip and then come back a touch. If you turn tightly you will need to trim down or you will lose grip. Of none of this affects speed etc you may well have too small a prop
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I was born not knowing and have had only a little time to change that here and there.
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31 May 2020, 18:41
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#3
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Member
Country: UK - England
Town: teesside
Boat name: magic
Make: humber 5.5
Length: 5m +
Engine: mariner 115
MMSI: 232012453
Join Date: Apr 2014
Posts: 1,558
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thanks but its doing it at quite low trim levels quarter on the gauge in a straight line. I will get a number off the prop tomorow
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31 May 2020, 18:55
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#4
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Member
Country: UK - England
Town: South Yorks
Boat name: Black Pig
Make: Ribcraft
Length: 5m +
Engine: DF140a
MMSI: 235111389
Join Date: Feb 2008
Posts: 12,178
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If your AV plate is 2” above the keel, it sounds a tad high. Try dropping a hole. It’s very much a trial & error to get things “just so” different engines/props/hulls all react differently.
What was your WOT RPM?
__________________
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: Don't feed the troll
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31 May 2020, 19:04
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#5
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Member
Country: UK - England
Town: teesside
Boat name: magic
Make: humber 5.5
Length: 5m +
Engine: mariner 115
MMSI: 232012453
Join Date: Apr 2014
Posts: 1,558
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hi thanks I haven't got that far yet its a brand new outboard and I'm just running it in so haven't had it flat out yet probably only has 2.5 hours on it ill be back out in it tomorrow another varied hour and ill give it a brief wot run . I was just surprised it started letting go at a relatively low trim out. thanks for the input
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31 May 2020, 22:10
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#6
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Member
Country: UK - Scotland
Town: north ayrshire
Boat name: charlie girl
Make: S/R5.4/regal3760
Length: 10m +
Engine: Suzukidf70 2x6lp 315
Join Date: Jul 2009
Posts: 4,027
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Quote:
Originally Posted by Pikey Dave
If your AV plate is 2” above the keel, it sounds a tad high. Try dropping a hole. It’s very much a trial & error to get things “just so” different engines/props/hulls all react differently.
What was your WOT RPM?
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[emoji106]my thoughts too
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01 June 2020, 20:24
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#7
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Member
Country: UK - England
Town: teesside
Boat name: magic
Make: humber 5.5
Length: 5m +
Engine: mariner 115
MMSI: 232012453
Join Date: Apr 2014
Posts: 1,558
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didn't get chance to do a wot run but the av plate is 2 1/2 inches above the keel line and It looks like if I drop the outboard onto the last hole the top one I will lower the outboard by an inch and a half so I think that's the way to go will give me an av plate an inch above the keel line. im doing nothing with the prop yet its a 15x17p which I think is recommended size for my mariner 115 ct
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01 June 2020, 21:23
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#8
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Member
Country: UK - Scotland
Town: Easdale
Boat name: Miss Isle
Make: Solent 6.9
Length: 6m +
Engine: 225 optimax
Join Date: Jan 2008
Posts: 1,427
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__________________
I was born not knowing and have had only a little time to change that here and there.
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01 June 2020, 23:09
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#9
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Member
Country: USA
Town: NorCal
Boat name: SHARKY
Make: AB
Length: 4m +
Engine: Honda BF75 & BF5
Join Date: Dec 2009
Posts: 2,108
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With the boat running at a decent speed the upper plate above the prop should be riding at the top of the water, but just touching the water. So if it is currently above the water the outboard needs to go down. Too deep and it will send spray everywhere. Too shallow and you will have cavitation issues.
Edited to clarify.
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02 June 2020, 06:38
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#10
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Member
Country: UK - England
Town: teesside
Boat name: magic
Make: humber 5.5
Length: 5m +
Engine: mariner 115
MMSI: 232012453
Join Date: Apr 2014
Posts: 1,558
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thanks folks im going to drop the outboard to the lowest setting should sort it
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02 June 2020, 08:44
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#11
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Member
Country: UK - England
Town: South Yorks
Boat name: Black Pig
Make: Ribcraft
Length: 5m +
Engine: DF140a
MMSI: 235111389
Join Date: Feb 2008
Posts: 12,178
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Quote:
Originally Posted by beerbelly
thanks folks im going to drop the outboard to the lowest setting should sort it
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Don’t go too low. I’d aim for just above the keel with the engine trimmed so that the AV plate is parallel with the keel. Use a long straight edge along the keel to check. The eye can be fooled, especially when the boat is sat on the trailer,
__________________
Rule#2: Never argue with an idiot. He'll drag you down to his level & then beat you with experience.
Rule#3: Tha' can't educate pork.
Rule#4: Don't feed the troll
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02 June 2020, 17:21
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#12
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Member
Country: UK - England
Town: teesside
Boat name: magic
Make: humber 5.5
Length: 5m +
Engine: mariner 115
MMSI: 232012453
Join Date: Apr 2014
Posts: 1,558
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Quote:
Originally Posted by Pikey Dave
Don’t go too low. I’d aim for just above the keel with the engine trimmed so that the AV plate is parallel with the keel. Use a long straight edge along the keel to check. The eye can be fooled, especially when the boat is sat on the trailer,
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I did check it with av plate parallel to the keel. the outboard is on its second from the top hole and the av plate measured with a long straight edge is approx. 60mm above the keel line it runs fine fully trimmed in straight and taking turns and fine in a straight line trimmed out until about quarter on the trim gauge where upon it starts slipping this is in a straight line on relatively flat water. I am proposing to lower the outboard onto the top holes in the outboard bracket to lower the outboard by approx. 20-25mm that is unfortunately as low as it will go but will still be 35-40mm above the keel line .I am hoping this will give the prop more bite and allow me to use more trim . thanks for everyone's input I do appreciate all advise
during a search on here to look for similar I found some posts a couple of years ago from Phil m and he was fitting out a new destroyer 5.8 with the same outboard I have and he was asking the same questions although he was worried his transom had been made too deep .anyway he mounted his on its lowest setting and said it was fine no issues even though he was 35mm above the keel line so I am expecting to find the same
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02 June 2020, 18:14
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#13
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Member
Country: UK - Scotland
Town: Denny
Boat name: Highland Bluewater
Length: 6m +
Join Date: Mar 2013
Posts: 1,647
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Have you calibrated the Smartcraft trim gauge.
It's very badly explained in the manual because the only way you can establish where the "Max trim" is, is by trimming out as far as you can with the engine under moderate load, maybe max displacement speed, and save that, throttle back, turn the ignition off (the gauge will continue to register). Run the tilt all the way up and save that as the trailer position. As soon as you do that the gauges will reset and the normal trim position should come in around mid scale.
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02 June 2020, 18:40
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#14
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Member
Country: UK - England
Town: teesside
Boat name: magic
Make: humber 5.5
Length: 5m +
Engine: mariner 115
MMSI: 232012453
Join Date: Apr 2014
Posts: 1,558
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Quote:
Originally Posted by Last Tango
Have you calibrated the Smartcraft trim gauge.
It's very badly explained in the manual because the only way you can establish where the "Max trim" is, is by trimming out as far as you can with the engine under moderate load, maybe max displacement speed, and save that, throttle back, turn the ignition off (the gauge will continue to register). Run the tilt all the way up and save that as the trailer position. As soon as you do that the gauges will reset and the normal trim position should come in around mid scale.
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hi I don't have smart craft just the normal quicksilver rev counter and separate trim gauge
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