Just finished a repower of my 1998 Islander 268. Installed a Yamaha F250 with a 19T 15 1/4 prop. With full gas (134 gallons) I get about 39MPH and WOT maxes at 4900 RPM. Was looking for feedback on if these numbers for speed and WOT make sense. Love the engine, but after coming off 10 years of a OX66 with 5600 WOT and about 35 MPH, just wanted to get others opinions. Thoughts?
Repowered Islander 268
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Hookup1
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What percentage of your time is running at WOT? You have a 4-stroke that isn't going to rev that high. The more important issue getting the props right for mid-range performance. Waterline length helps you with top end speed. With a smaller boat you can rarely use that speed. Check out my results...
www.greatgrady.com
Check your planing speed at mid-range RPM's and different sea condition. I dropped 2" of pitch and went to a 4-blade prop. It was game changes. Props were slipping a lot. PropGods.com recommended these. No loss of red line speed. Never checked WOT before or after - its only useful to see how much headroom you have on prop loading. Able to plane at lower speeds and not fall off.
Sounds like the the engine is a good choice - single V6 block less weight then 2 x 150's straight 4's like I have. If you really want an opinion get your numbers together and call Ken at PropGods.com. It's free.
New to Us Islander, what Props are you Running, Twin F150's
Well I sold my 1999 272 Sailfish this spring due to a newborn and figured it would not get too much use. I planned on just using my fathers 180 Sportsman for a few years until I would upgrade to a newer Sailfish or Marlin. We did not remain boatels as long as we anticipated, we came across a...
www.greatgrady.com
Check your planing speed at mid-range RPM's and different sea condition. I dropped 2" of pitch and went to a 4-blade prop. It was game changes. Props were slipping a lot. PropGods.com recommended these. No loss of red line speed. Never checked WOT before or after - its only useful to see how much headroom you have on prop loading. Able to plane at lower speeds and not fall off.
Sounds like the the engine is a good choice - single V6 block less weight then 2 x 150's straight 4's like I have. If you really want an opinion get your numbers together and call Ken at PropGods.com. It's free.
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deepdesire
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Patsy Mac, I have a 96 268 Islander with a 2019 Suzuki 300 AP. The new Suzuki props were limited to a minimum pitch of 17". I used to have a single Yammi 250 and ran a 15 x 15 prop. My Islander is heavy with hardtop, enclosure, lots of gear, at 5100 rpm she would run about 31 mph. The new 300 with the 16 dia x 17pitch prop gave a horrible holeshot, but the top end was something I never experienced with my Yamaha. The Suzuki would only spin up to about 4750 rpm but she was going about 39 mph. The new Suzuki has a wot of 6200 rpm so the 17p was too much prop. After several trips to the prop shop we ended up with a 14 1/2 pitch full cupped 16" dia wheel. My wot speed is around 34 at 6000, at 4600 about 24mph and depending on sea conditions 1.9 to 2.4 mpg. I would think that 4900 rpm is too low for your F250 and that 19p is way too much pitch. You have to be able to spin up close to your wot range or you are working your engine way too hard drastically shortening its life.
Hookup1
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DeepDesire has it right. Talk to PropGods.com to see what they recommend. All three of us are running 268 Islanders.
Hookup1
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What was the pitch on the OX66 prop?
Yamaha specs on V6 4.2L 250 hp. I think you are over propped.
| Prop Shaft Horsepower | 250hp at 5500 rpm |
|---|---|
| Full Throttle RPM Range | 5000 ~ 6000 rpm |
Thanks all, great info and I will contact Propgods.com. My old OX66 was running a 15 1/4 x15P prop, had great hole shot up onto plane (perhaps because of two stroke). I still have that prop, wonder if I should throw it on and take her for a run.
Hookup1
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See what Prop Gods have to say. As long as the prop fits I don't see anything wrong with trying it out. Try testing different RPM's in both directions with the current to determine where you can stay up on plane. Also speed at red-line and WOT RPM's but don't go over 6,000.
Update, Prop Gods recommend trying out my old 15 inch prop. Will let you know how it changes performance.
Thanks, with advice, we are going to try a 15" pitch and post how it goes. Great feedback, Thanks.
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deepdesire
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Years ago I spoke with PropGods. They recommended a four blade wheel and recommended a 14 Pitch. I am not concerned with top speed as much as I am increasing my range and fuel efficiency. Repowering has given me both of my objectives and the confidence that goes with new power. Invest the time and change wheels until you get whats best for your hull and engine
efx
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It’s an interesting combination of a single engine on a 268. The boat is long and narrow. Seems like a single engine may have its place to lighten up the stern. For reference I have twin f150, installed 2020 and wot is 5900 and 46 mph. It on a non bottom painted 1999 with only one main fuel tank and hardtop.
I got 53mph out of my ‘95 Islander with twin 200 HPDIs at around 5200 rpm. Never fully opened it up. I would cruise around 28 knots at 3600 burning 14.7gph.