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Propeller choice + Guard

R

rolfroyal

New member
Hello

New here with a question that probably very basic here, but are nevertheless hoping for a response.

I have a 30" sailing trimaran weighing in at just under 2500kg before human additions.
This is pushed by an extra long leg 8hp Honda outboard from 2018 and would like to change the factory propeller as the engine reverses badly and overall can use all the thrust I can get.

There is a recommendation to use the PolaStorm 10" x 5" High Thrust Aliuminium prop. There is also a 10" x 7" version of this. I do not know the difference?
What to choose? https://www.ebay.co.uk/itm/144273166350

And are any of these ok for the engine? Never run full RPM (10sec max).

In addition I am thinking of adding a guard to protect the propeller and to (supposedly) aid thrust and fuel economy: https://tinyurl.com/dk2zcm73

Thank you very much in advance!

Rolf
 
Hi Rolf,

Honda sells high thrust props. You might want to look at those too.

I have no knowledge of the Pola Storm props and I really don't have a recommendation as to what might work best for you.

Although, I'm guessing you need more "bite" for reversing so the bigger pitch...7""...might be the one I would choose. But...that is ONLY.A GUESS!

What does jump out at me though is that, in the link you sent for the prop guard, it is listed as a 9". If you plan on using a 10" diameter prop, I don't think that's going to work.

Good luck.
 
Hi!

Thank you very much for your response. Bigger pitch does sound better as I am valuing grunt in tight labour manoeuvres over an extra knot on top speed.

And well spotted, you are very right, that guard won't work.

Many thonks,

Rolf
 
Ha!
Funny because I read Harbour, not labour.

I would have never known had you not pointed that out.

Interesting how the mind works and how spell check often doesn't! :>)
 
And are any of these ok for the engine? Never run full RPM (10sec max).

You might want to consider running your engine at WOT occasionally. Never hurts to get the engine up to operating temperature, keep the carbon buildup to a minimum.
 
Ok, yes, makes sense. Thanks!

There are times where I run it at 30-40% for up to an hour, when there is no wind. Will this do the job of getting it to operating temp?
Or will only full throttle do this?
 
Rolf,

Just my opinion but 40% for an hour should definitely have the engine to operating temperature for most of that time.

But I would still recommend occasionally running above 75% throttle for a few minutes to properly "excersise" the engine.

Fuel additives can help alot with keeping deposits down. I use Chevron Techron Plus Marine Fuel Additive but you might have a different preference.

Also, I suggest NOT running the engine at one constant throttle setting for extended periods. It's best to vary engine rpm over a long run.

Again, just my opinion.
 
Our fire rescue boat has twin 135’s, we run prop guards like those during lobster fishing season to avoid getting caught up in the buoy marker lines. They knock 20% or more off top speed and also make the steering very touchy, a small change of direction in steering can make for a sudden unexpectedly large change of direction. This is on a 25 foot Boston Whaler hull, so apples and oranges comparison.

I would suggest you change one thing at a time to assess the benefits of the change and do the prop first. Not sure if a good prop site would have recommendations for your situation or not, some have a program to input details on boat and engine and make pitch/prop recommendations.
 
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