[pshrubb]

I'm trying to figure out if I am using the correct props on my boat.
I have a 188 36 Open with a tower and am running Caterpillar 3208s.
Presently I have 4 blade 21x24 props.
The engine don't seem to get up to full rmps.
Any advice?

[sbw1]

I'm trying to figure out if I am using the correct props on my boat.
I have a 188 36 Open with a tower and am running Caterpillar 3208s.
Presently I have 4 blade 21x24 props.
The engine don't seem to get up to full rmps.
Any advice?

You could contact Tiara and ask them for help. Being over propped will ruin those nice diesel engines so you need to get this issue fixed. Lay off the high load power settings until you find some wheels that will allow you to achieve the manufacturer WOT spec for the 3208s.

[jclark003]

absolutely correct. Overloading diesels, really at any rpm will shorten engine life, sometimes dramatically. hard to give advice without more details and knowing how far off you are.  a couple of quick things to do are check that your bottom is clean and you aren't dragging something in your running gear. Also check/replace fuel filters and air filters as either one can cause your engines to not achieve rated speed. excess smoke or soot may point to a mechanical issue and a visit from Cat especially if you are way off at the top and or the problem is progressing. 

If memory serves a 375hp 3208 is rated at 2800 so 2830-2850 is a good wot rpm range. 

Good luck. 

[pshrubb]

Thanks for your reply.
I have an opportunity to get a couple of 20x24 props at a good price.
I'd rather keep the same diameter as I have now and try 21x23 or 21x22 but I'm reluctant to spend the money not knowing for sure if this will improve performance and engine life.

[jclark003]

Understood. I would trying to ascertain if you even have a prop problem before going down the path of purchasing another set. If your problem is prop related from a financial point of view you may be better off having your current props worked over as opposed to putting another set on the boat and quite possibly sending them in to be worked. Of course this depends on the age and condition of your existing props and whether it is worth it to work them over (compounding problems). 

If you can record and post your WOT RPM and speed readings. Let the engines run at WOT for a minute or two to clean things out and build up speed. If you are way off the top or you have one engine dragging then it may not be prop related (unless you have added a lot of weight or a tower which would lean me more towards a prop issue). With that data a reputable prop shop can probably tell you over the phone if your props can be worked to get you to your desired engine speed or if not, what would be a good starting point in terms of pitch and diameter.

[sbw1]

Thanks for your reply.
I have an opportunity to get a couple of 20x24 props at a good price.
I'd rather keep the same diameter as I have now and try 21x23 or 21x22 but I'm reluctant to spend the money not knowing for sure if this will improve performance and engine life.

There really is no such thing as a good price on the wrong props. If you are over propped with the current wheels, those will be the most expensive props you will ever run. The new ones, same thing. This is an issue you have to get right. The suggestion to call CAT for advise is a good one. They have a computer system that will provide you with info on the health of your engines, and their techs can answer your technical questions. Achieving the proper WOT is one key to not destroying your engines by overloading them. CAT can help you with the other important things to do for engine longevity.