Optimax 90 S.S. prop suggestions

canadianfcat

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May 18, 2011
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14
So currently I'm running a 2006 Optimax 90 hp. with a 13' prop with 19 pitch( Alloy ) ..with a fin.
I'm getting under perfect conditions and only one person in boat 38 mph at 5600 rpm trimmed on the end of pushing air ...any chop or wind 32-34 at 3400 rpm.
My boat is a 1992 Starcraft SFM 17.

I've got a couple options or thoughts but could use some advise.
 

Sea Rider

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Sep 20, 2008
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Why do you like boating with trim all the way up ? riding that way, doel fin will achieve more water drag on it. Ideal is for boat to ride parallel to water level with trim set at 90 for fin, cav plate to ride same. Check that way and report back if having better water performance.

Happy Boating
 

canadianfcat

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May 18, 2011
Messages
14
That's how the boat runs fastest ..when trimmed out. I stop trimming when speed doesn't increase .

If trimmed down it really lists to the right ..As soon as I trim it up a bit rolls back to left and level.
 

Sea Rider

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What's the max wot rpm range of that 90, 5000-6000 RPM ?

Happy Boating
 

canadianfcat

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May 18, 2011
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The boat also came with a 17 pitch prop (alloy.. maybe the original?) ..How does a lower pitch affect performance ..?
 

Sea Rider

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If with a 19 pitch while lightly loaded OB achieves 5600 wot revs, going 2 less in pitch to a 17, OB will surely over rev, how much, isn't known till you test that prop in equal water conditions. Do you plan boating constantly by yourself ? If with 19 pitch, bear in mind that as soon you add more weight, wot revs will decrease accordingly.

OTOH, if over revving with a 17 pitch, with added weight wot rpm will decrease too. As of right now, with a 19 pitch OB is just 150 wot revs from max 5750. A 17 pitch will have better hole shot with slight less top end speed when boating with more passengers. Not ideal for solo boating though.

Happy Boating
 
Last edited:

Texasmark

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I think you are doing ok. Having run several engines over the years on boats on the 16-18' range, glass and alum, flat, semi-v and pad boats, 38 is a respectable speed for that engine. In answering Sea Rider's comment, (opinion) after following his posts for a year or so, he runs in a different environment that I ran. He runs RIB boats and big water, big waves all that where what he says matters. For me, I ran right at "blowout" trimmed out as far as she would go, right at the point where the rpms started an abrupt increase and the mph started to fall off.

My avatar is a 17' with a 90, 5800 rpm gps 49. To get that I had a stepped hull minimizing hull drag, just running on the center "pad" portion like pads on bass boats, and was running a 24P Ballistic XP SS with all the amenities of a quality SS prop. Engine was up one mounting hole off the transom putting the AV plate just above the water surface; (more drag reduction). You can't get there with an "alloy" (assuming that means cast alum). Your gear ratio is 2.33 and your rpms are at the tip of your recommended rpm. I like to run there; engines love it. Also, you can't get there with a lot of wetted surface....aka hull to water contact, with that size engine on that size boat........at least I haven't been able to; course I haven't made it my life long ambition either. Grin. Just fooling around pastime.





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Sea Rider

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In answering Sea Rider's comment, (opinion) after following his posts for a year or so, he runs in a different environment that I ran. He runs RIB boats and big water, big waves all that where what he says matters. For me, I ran right at "blowout" trimmed out as far as she would go, right at the point where the rpms started an abrupt increase and the mph started to fall off.

Some constructive clarifications & precisions :

Never said I boat al high water, big waves conditions. Although could go boating off coast is still at near plain flat water cond with min wind and no waves at all, on rare occasions some light swell to have fun surfing with.

Although we sell Tohatsu OB's mainly for Sibs/Ribs have rigged many different type of boats with the sweet OB/transom height dialed as stated on many posts. New boat owners boating to their full content.

Running an OB with doel fins attached other than riding parallel to water level will achieve doel fin water drag, more the larger. Very notorious on less HP or underpowered OB's.

To understand what have mentioned : Go for a car ride on a highway, open your window, Pull half arm out with hand riding parallel to highway, slowly rotate hand upwards, then downwards, what do you feel ? excessive hand drag, with near no drag compared to when hand rides parallel, right ? Check for yourself. Now imagine a doel fin riding on water that's 1K denser than air duplicating same air examples.

The issue about running parallel to water level while OB is trimmed to 90? with deck weight evenly distributed it's mentioned on every boat and engine Owner's Manual have had the chance to read about. It's not my invention. This cond only works fantastic if matched with spot on OB height seated on transom and if being exquisite with a prop maximization.

The issue about running excessively trimmed up is the bow rise attitute boat will achieve along unstable hull behaviour at speed along heavily hull banging. Much worse with badly deck weight distribution while riding on choppy, windy water cond that could be dangerous for other boaters sharing the ride with exception of the driver.

Texasmark, I'll bet you that as you like running your boat, wil have awfull water performance on choppy, windy cond and at tight close turns at speed. That setting only works "well" on flat calm, no wind water cond and at straight water courses and racing if pasionate doing that.

For recreational, newly or family oriented boating it's the wrong way to go.

Happy Boating
 

Texasmark

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Joined
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Messages
14,798
Some constructive clarifications & precisions :

Never said I boat al high water, big waves conditions. Although could go boating off coast is still at near plain flat water cond with min wind and no waves at all, on rare occasions some light swell to have fun surfing with.

Although we sell Tohatsu OB's mainly for Sibs/Ribs have rigged many different type of boats with the sweet OB/transom height dialed as stated on many posts. New boat owners boating to their full content.

Running an OB with doel fins attached other than riding parallel to water level will achieve doel fin water drag, more the larger. Very notorious on less HP or underpowered OB's.

To understand what have mentioned : Go for a car ride on a highway, open your window, Pull half arm out with hand riding parallel to highway, slowly rotate hand upwards, then downwards, what do you feel ? excessive hand drag, with near no drag compared to when hand rides parallel, right ? Check for yourself. Now imagine a doel fin riding on water that's 1K denser than air duplicating same air examples.

The issue about running parallel to water level while OB is trimmed to 90? with deck weight evenly distributed it's mentioned on every boat and engine Owner's Manual have had the chance to read about. It's not my invention. This cond only works fantastic if matched with spot on OB height seated on transom and if being exquisite with a prop maximization.

The issue about running excessively trimmed up is the bow rise attitute boat will achieve along unstable hull behaviour at speed along heavily hull banging. Much worse with badly deck weight distribution while riding on choppy, windy water cond that could be dangerous for other boaters sharing the ride with exception of the driver.

Texasmark, I'll bet you that as you like running your boat, wil have awfull water performance on choppy, windy cond and at tight close turns at speed. That setting only works "well" on flat calm, no wind water cond and at straight water courses and racing if pasionate doing that.

For recreational, newly or family oriented boating it's the wrong way to go.

Happy Boating

"Texasmark, I'll bet you that as you like running your boat, wil have awfull water performance on choppy, windy cond and at tight close turns at speed. That setting only works "well" on flat calm, no wind water cond and at straight water courses and racing if pasionate doing that."

Well sir, what was the water condition in my Avatar? Answer your question?
Iterating, the comments I made were clearly marked (Opinion) based upon your previous comments on postings of others that I have read.

If you have noticed my deep, rough water, heavy loaded, moderate speed boat comments, they follow the same tried and true tradition as you "seem" to adhere. The point here is that the tried and true tradition does not always apply and that's the basis for my "go fast" with stock equipment comments. It's just cheap entertainment that's just fun......like riding a stock motorcycle with no windshield and no helmet on a West Texas or Arizona highway....long and straight and no traffic.....with no posted speed limit.
 

Sea Rider

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Well, I'm not a fortune teller about your avatar pic. Glad to know that both run on flat calm no wind water cond, what works for me works for you too. At least you're in agreement that that superb boating of yours is only possible on that stated water cond.

Happy Boating
 

Texasmark

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Joined
Dec 20, 2005
Messages
14,798
Well, I'm not a fortune teller about your avatar pic. Glad to know that both run on flat calm no wind water cond, what works for me works for you too. At least you're in agreement that that superb boating of yours is only possible on that stated water cond.

Happy Boating

Well sir if there were any chop it would have broken up the wake.
 
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