Motors again - 70-90hp

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Post Options Post Options   Likes (0) Likes(0)   Quote terrafish Quote  Post ReplyReply Direct Link To This Post Posted: 16 Jul 2018 at 10:40pm
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Re wedging the motor
Whats the cons on doing this. would like a few more degrees bow down on the ****ty b.o.i sw . Gotta fleetline solitaire with a suzi df90.
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Post Options Post Options   Likes (0) Likes(0)   Quote Steps Quote  Post ReplyReply Direct Link To This Post Posted: 17 Jul 2018 at 9:27am
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I found my boat with 3 pob, approx 2000kg, gotup and went fine with 130 hp

2000kg / 130 hp  those numbers correct?
That would be a 6m plus trailer boat??
WoT speed around 30/32 mph  most prob a prop around 15" and about a 20/22 mph cruise speed,  only just on the plain

Re wedging the motor
Whats the cons on doing this. would like a few more degrees bow down on the ****ty b.o.i sw . Gotta fleetline solitaire with a suzi df90.

1/ Why do you think needs wedging?
2/ doesnt the motor have tilt trim?
3/ may find a 4 blade or a prop with more rake would sort high bow/ porpoising issue

Thats assuming the engine is mounted correct height and current prop is in ball park or correct...
More likely they are not, and thats your base issue.
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Post Options Post Options   Likes (0) Likes(0)   Quote MikeAqua Quote  Post ReplyReply Direct Link To This Post Posted: 17 Jul 2018 at 4:39pm
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Originally posted by Steps Steps wrote:



about a 20/22 mph cruise speed,  only just on the plain



My 6m trailer boat will plane at <15 mph - not if it was at 2,000kg though ...

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Post Options Post Options   Likes (0) Likes(0)   Quote terrafish Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2018 at 6:51pm
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When I go solo I tend to bounce a bit more, with 2 or three pob, smooth as, and can trim motor up a bit from hard down, unless its particularly grotty. prop is at low end of min rev wot, 5250rpm 14x19, 28kn, 4000rpm cruise 20kn, spare prop 6200rpm wot still 28kn 4400rpm cruise 17/18kn and fuel consumption higher thru all rev range, prop stamped 14k.Engine is mounted correctly, could have gone one hole higher but this would have reduced my rough water capabilitys by causing more potential cavitation. Dunno if another prop would get past her royal pain in the arse, sorry meant Highness!.
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Post Options Post Options   Likes (0) Likes(0)   Quote Big -Dave Quote  Post ReplyReply Direct Link To This Post Posted: 18 Jul 2018 at 11:50pm
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Originally posted by Steps Steps wrote:

<span style="line-height: 17.1429px; : rgb251, 251, 253;">I found my boat with 3 pob, approx 2000kg, gotup and went fine with 130 hp</span>
<span style="line-height: 17.1429px; : rgb251, 251, 253;">
</span>
<span style="line-height: 17.1429px; : rgb251, 251, 253;">2000kg / 130 hp  those numbers correct?</span>
<span style="line-height: 17.1429px; : rgb251, 251, 253;">That would be a 6m plus trailer boat??</span>
<span style="line-height: 17.1429px; : rgb251, 251, 253;">WoT speed around 30/32 mph  most prob a prop around 15" and about a 20/22 mph cruise speed,  only just on the plain
</span>
<span style="line-height: 17.1429px; : rgb251, 251, 253;">
</span>
<span style="line-height: 17.1429px; : rgb251, 251, 253;">Re wedging the motor</span><br style="-sizing: border-; line-height: 17.1429px; : rgb251, 251, 253;"><span style="line-height: 17.1429px; : rgb251, 251, 253;">Whats the cons on doing this. would like a few more degrees bow down on the ****ty b.o.i sw . Gotta fleetline solitaire with a suzi df90.</span>
<span style="line-height: 17.1429px; : rgb251, 251, 253;">
</span>
<span style="line-height: 17.1429px; : rgb251, 251, 253;">1/ Why do you think needs wedging?</span>
<span style="line-height: 17.1429px; : rgb251, 251, 253;">2/ doesnt the motor have tilt trim?</span>
<span style=": rgb251, 251, 253;"><span style="line-height: 17.1429px;">3/ may find a 4 blade or a prop with more rake would sort high bow/ porpoising issue</span></span>
<span style=": rgb251, 251, 253;"><span style="line-height: 17.1429px;">
</span></span>
<span style=": rgb251, 251, 253;"><span style="line-height: 17.1429px;">Thats assuming the engine is mounted correct height and current prop is in ball park or correct...</span></span>
<span style=": rgb251, 251, 253;"><span style="line-height: 17.1429px;">More likely they are not, and thats your base issue.</span></span>
i have weighed the boat and trailer. at 2 tonne. the trailer is around 300 kg. i weigh 140, my normal passengers are around the 80 kg mark each. so we are back up to 2 tonne. it had a 17 inch vengeance prop, and 60kmh was easily achievable most days. Planing speed was around 18kmh. easy cruise was 40 to 50 kmh. 40 kmh was a fuel burn of .7l per km. hull length 6 m.
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: 19 Jul 2018 at 10:59am
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When I go solo I tend to bounce a bit more, with 2 or three pob, smooth as, and can trim motor up a bit from hard down,...

 So you have trim with more weight? none when on your own? assume gear is loaded towards the bow?
 If dont have any trim solo, then indicates that the engine needs adjusting/ shimming further 'trimmed ' down....or putting another way is not trimmed down far enough ...
 OR having a prop with not enough rake to lever the bow down will do the same...
Crunching numbers
prop is at low end of min rev wot, 5250rpm 
 prop 14x19, 28kn,
 Suzt DF90A gearbox 2.59:1. 
Thats a WoT slip around 12%
you should be targeting around 5%...
 4000rpm cruise 20kn,
 17% slip should be targeting 12 to 15% slip @ cruise.
have an issue with the prop diam/ cupping or number blades.. need more grip
More grip will drop the WoT rpms even further so will need to drop pitch down also.
 
You should targeting the lower end with your normal full loaded boat.. which when the boat is not loaded still have WoT around 3/4 + of the way to the top

 spare prop 6200rpm wot still 28kn
 Slip 26%
 4400rpm cruise 17/18kn
 and fuel consumption higher thru all rev range, 
 Hell yeah , like driving a car reving its heart out with a clutch thats slipping bad and going nowhere

 wot still 28kn 
 This is very significant.. most ppl believe a change of prop will change the WoT speed of a given weight with a given hp will change.. it doesnt.. @ woT the engine is at max hp 90hp.. that will only move a given weight at a given speed..basic high school physics.

Taking the 1st prop as basis.. decreasing slip to 5% and targeting just below the mid WoT rpm spec (5800)  5700 rpm  you need a 16" pitch
This will give WoT the same and cruise 20/22 mph

 And I would be looking at a 4 blade, these usually have far more rake that brings the bow down...  because the 'thrust' cone behind the prop is narrower, it breaks water surface further back, cavitation reduced....
With current prop, if the cone breaks water too close to the prop, it looses the push at the top, and the extra push at the bottom levers the bow up.....
 The 4 blade also provides more grip, and would be looking at one around 13 1/4 to 13 3/4 diameter...

 Sry the red txt will not change

i have weighed the boat and trailer. at 2 tonne. the trailer is around 300 kg. i weigh 140, my normal passengers are around the 80 kg mark each. so we are back up to 2 tonne. it had a 17 inch vengeance prop, and 60kmh was easily achievable most days. Planing speed was around 18kmh. easy cruise was 40 to 50 kmh. 40 kmh was a fuel burn of .7l per km. hull length 6 m.
 2 tonne. it had a 17 inch vengeance prop, and 60kmh was easily achievable most days. Planing speed was around 18kmh. easy cruise was 40 to 50 kmh. 40 kmh was a fuel burn of .7l per km. hull length 6 m.

 Most 6m boats gross weight  on the water around the 1750/ 2000 kg max.
60km/hr is 37 mph
For 130hp move a given weight (trailer boat planing hull) on water would make the boat approx  1650kg.
 Cruise of 40km (25mph) for a 2T boat would require 73 hp at the cruise rpms, and ideally another 10 to 15% reserve power for performce in chop so doesnt fall off plain when stalls on next wave.

hull length 6 m... this is from bow base to bottom of hull ..not any duckboards etc?  ie a buccaneer 635 bis actually closer to 6m hull.











 

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Post Options Post Options   Likes (0) Likes(0)   Quote Dmnz Quote  Post ReplyReply Direct Link To This Post Posted: 03 Nov 2018 at 7:31am
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Hay there legsgetem ....did you purchase the exreme 500? If not yet consider the Suzuki 90. Very light in comparison
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Post Options Post Options   Likes (0) Likes(0)   Quote letsgetem Quote  Post ReplyReply Direct Link To This Post Posted: 03 Nov 2018 at 9:12am
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I have just bought a new Figlass Firestar 530. That's going from alloy Stabi to fibreglass. Big change - mainly in looks and keeping it clean.
 
Motor's a mercury 4s 90hp. I went on a trial with that motor and was impressed how efficient it was, ie went faster at lower revs than I expected, given the theoretical power to weight ratio. I am wondering if the fibreglass is more efficient than alloy - eg smoother and less friction. Also, I think the Stabi pontoon shapes result in more drag.
 
I was interested in the extreme 500, but decided against it due to -
- doubt it would tolerate the weight of a 90hp on the back
- cabin rather low, so could not sit up in it; making getting in and out hard.
- very expensive I thought - would cost about $8000 more than the Figlass Firestar I ended up with
 
I chose the Firestar, due to -
- generally good comments about them
-  deadrise 21 deg (same as the Extreme).
- beam 2.1m, modest, so doesn't make the trailer too wide for me - trailer width ended up 2190
- bigger, longer at 5.3m, heavier but towing weight about 950kg which is fine.
- lateral stability will be a bit worse than a pontoon; but seems reasonable to me. The 80L underfloor tank will help ballast. 
- cabin relatively large for its size. I suppose that seems odd for a fishing machine - but I want to be able to get in the cabin to rest and shelter from wind and sun and rain. The outside space in the cockpit, is enough for me - I don't want any more length outside .
- lovely seats - most impressed - thick padding., side support, 360 swivel, for & aft adjust, height adjust, soft ride suspension. Wow, best seats Ive seen on any trailer boat. I can actually get seat position exactly as I want.
- reasonable price - cost $47,000, including a winch (Viper 1000) and anchor costing $2,700
- seemed prepared to customise things I want. mainly - no carpets! on walls or floor. Walls are finshed in grey paint, looks ok. I painted the floor with anti-slip paint.
 
I chose the Mercury 4s 90hp, due to -
- have heard relatively favourable things about the latest Mercs.
- weight at 165kg is slightly more than Suzuki at 156, but not enough to matter to me
- there are 3 options for getting service - 2 on Hibiscus and 1 at Albany.
- on the sea trial, I thought the Merc was noticeably quieter than my Honda 60hp. Time will tell if Ive made a good choice eh!!! 
 
To recap, my main objective is to get significantly softer riding in chop; the Stabi is too hard for my taste. The Firestar - is heavier by about 40%, and has a sharper hull (deadrise 21 compared 17 deg on the Stabi). I haven't yet been out on its first fishing trip.
 
 For the record, there are a couple of things I don't like about the Firestar -
- doesn't have a bowsprit. Odd. I think the anchor retrieval could hit the fibreglass bow and damage it; and with a winch, stowing the anchor on the bow, requires a bowsprit. I got one made in Stainless steel, that's fine, but cost $621!
- cockpit side shelves are too narrow, hold bugger all. Compared to a pontoon hull that has excellent wide side shelves.
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Post Options Post Options   Likes (0) Likes(0)   Quote Norseman Quote  Post ReplyReply Direct Link To This Post Posted: 03 Nov 2018 at 3:23pm
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Give a look at the Tohatsu 90hp TLDI two stroke direct injection at 153kg


"Nothing is so strong as gentleness, nothing so gentle as real strength." St. Francis de Sales
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