[RI Tiara]

I have a 1987 3300 flybridge with 454 crusaders and I have a dilemna. Original factory test sheet shows 18x19x3 blade props and the performance figures look spot on. When I bought the boat it had 18x21x4 blades on it (for the 8 years the previous owner had it). So an additional blade AND more pitch doesn't seem right to me. Handles and cruises nice but won't pull past 3800 (thats low), tops out about 30mph (seems OK), and seems a little down on mileage. I'm thinking I need to reprop to similar as from the factory. I run the boat at a steady cruise between 2800 and 3100. At 3000 she cruises about 22-24mph. No delusions that this is a fast or fuel efficient boat but I am wondering if a re-prop is worth it. These figures are similar at cruise to those I have seen others post when selling similar boats. No expertise in this area! Suggestions?

[trit21]

Boats should be propped so that under full load (boat full loaded, fuel fuel, water etc) the engine should turn up to rated RPM. So, find your rated RPM for the engines and compare that to the 3800 MAX she turns now. I think gassers normally turn at 4800 MAX so if that is the case, then you are WAY over propped. An over propped boat puts a lot of strain on the engines overloading them at all RPM levels. If I was you:

1) Find max rpm for you engines.
2) Adjust props to achieve at least the rated RPM. You will find the boat and engines are much happier and you may even get better range, etc. 

[Chris Burkard]

You are over-propped! Being over-propped adds stress to the engines, shafts and transmissions and reduces efficiency and long term can cause premature engine and transmission failure.

I believe your engines should turn at WOT under a load, a minimum of 4000 and a maximum of 4400 (please verify this as I am going off of memory). Tiara usually propped the boats to achieve a WOT throttle with a moderate load (full fuel, water, 2 people and 400 lbs. of gear to reach somewhere in the middle (4200 RPM). This way if you are running lite (low on fuel) you won't be able to over rev the engines and if you run loaded down with full fuel and 6 or 7 passengers plus gear you won't overload the engine engines.

If the recommended WOT range is 4000 to 4400 RPM, I would shoot for 4200 with a moderate load just as Tiara originally did.

My guess is you need 18x18-4s or 18/17-4s, but a prop shop will be able to give you a better estimate. I'm not sure that you can remove 3 or 4 inches of pitch from a prop so that can use your existing props. I know they can be adjusted about 1 or so inches either way. The rule of thumb for a vessel of this size is 1 inch of pitch equals approximately 100 RPM. You may be looking at purchasing new props.

Good Luck and let us know how it works out. 

[RI Tiara]

Thanks guys. I thought rule of thumb was 200 rpms per inch of pitch, but either way I have a buddy that also owns a Tiara. Slightly bigger boat but very similar in year and engine. He upgraded his engines and want to try a bigger prop. I'm hoping he has the same props I originally had so we can do an even swap. We will see!

You are over-propped! Being over-propped adds stress to the engines, shafts and transmissions and reduces efficiency and long term can cause premature engine and transmission failure.

I believe your engines should turn at WOT under a load, a minimum of 4000 and a maximum of 4400 (please verify this as I am going off of memory). Tiara usually propped the boats to achieve a WOT throttle with a moderate load (full fuel, water, 2 people and 400 lbs. of gear to reach somewhere in the middle (4200 RPM). This way if you are running lite (low on fuel) you won't be able to over rev the engines and if you run loaded down with full fuel and 6 or 7 passengers plus gear you won't overload the engine engines.

If the recommended WOT range is 4000 to 4400 RPM, I would shoot for 4200 with a moderate load just as Tiara originally did.

My guess is you need 18x18-4s or 18/17-4s, but a prop shop will be able to give you a better estimate. I'm not sure that you can remove 3 or 4 inches of pitch from a prop so that can use your existing props. I know they can be adjusted about 1 or so inches either way. The rule of thumb for a vessel of this size is 1 inch of pitch equals approximately 100 RPM. You may be looking at purchasing new props.

Good Luck and let us know how it works out.