My twin boat with Suzuki DF200 with 3x16x20 props has poor hole shot - help?

[Pioneer320]

My AlDhaen Pioneer 320 with twin Suzuki DF200 with 3x16x20 props has poor hole shot, should I (i)lower pitch, (ii) go to 4 blades (iii) add hydrofoils - or all three?

The hull is a 32ft AlDhaen Pioneer 320, displacement 5,500 kgs (inc engines) Boat is stern heavy due to Genset, 4 Batteries, Diesel Tank, Petrol Tank and Water Tank

I have twin twin Suzuki DF200 with 3x16x20 props.

When accelerating without trim tabs down in normal seas (wave height 0.5m to 1m) the boat struggles to plane if there are any more than 2 passengers. If any passengers sit in back seat ? it will not plane. Heavy cavitation /propeller slippage at around 14knts. Bow rises, stern digs deeply down engine revs sharply to over 5000 speed drops to 8kts.

With trim tabs fully down it only just comes out of hole onto plane in calm seas and struggles out the hole at all on heavier seas.

If boat has 2-3 adults on board and is full and/or waves are any higher than 1m+ boat will not plane unless passengers sit on front deck and trim tabs are full down ? and then only just comes out on plane.

Engines are fully serviced - no issues on prop or engine.

Once on plane - top speed is 39kts with WOT (Wide Open Throttle) ? Revs around 5800

 

[Texasmark]

Re: My twin boat with Suzuki DF200 with 3x16x20 props has poor hole shot - help?

I'm not a guy familiar with that size rig but here are a couple of things to consider....since no one answered you.

The fact that you run 5800 at WOT once you get up and running tells me you have the right prop pitch, or close to it.

You did not say whether or not you are running SS props with cupped trailing edges. Cupping helps to reduce cavitation, like you said you experienced at 14k, which I suppose is just about the time you get on plane; course if your boat is a deep V with a high dead rist at the stern, "on plane" is harder to detect and by the way, high deadrise at the stern is great for a soft ride in open water, but is very bad on trying to get out of the hole....but you can't change that.

Any time you are stern heavy you need to consider things that make the stern rise. Selecting a "stern lifting" prop for starters; 4 blades to help deliver the thrust if your engines have the torque to spin them and apparently they do; trim tabs in the full down position, all help. Engine trim needs to be fully tucked in.

If you don't have the torque to spin the prop in the hole and get your rpms up so that you can develop your available HP, ports in the prop help to do that......holes in the outer drum of the prop hub just below and behind the leading edge of each blade. They allow exhaust gasses to flow over the blades reducing the density of the medium and thus reduce the amount of hp required to do what you are doing at the time. This allows the rpms to raise under the lighter load thus getting your HP up faster since rpms are one part of the HP equation (torque and a constant of proportionality are the other 2). Apparently they came into being back when the larger bass boats started arriving with all their stern weight, assisting in getting out of the hole first and getting to the "honey hole" before your buddy.

I ran/run ported props and they work bigtime. The larger the hole the more the "slip". Size is right when the rpms come up a few hundred in the hole and then soon after planing out, they drop back down....like using overdrive on a stick shift automobile. Only thing that may be a problem is if the right conditions exist in rough water with the trim out too far would be slight ventilation....rpms would rise slightly. Usually if this happens, tucking in the trim till it stops solves the problem.

HTH,
Mark

 

[Texasmark]

Re: My twin boat with Suzuki DF200 with 3x16x20 props has poor hole shot - help?

Yesterday I incorrectly used the word "cavitation". I tried to edit today but it wouldn't work. So here is my rewrite:

Cupping helps to stop "ventilation", the sucking in of air when the blades are close to the surface resulting in reduced speed and increased rpms. Example would be under identical situations in a tight turn, a non cupped prop that was "blowing out" (ventilating) could be made to stop it by just cupping the trailing edge of the prop. BTDT

Until I got to this site ventilation was not mentioned. We always referred to the plate above the prop as the "anti-cavitation" plate, which I accurately learned on here it is not. After a life of using the term it takes concentration to keep my terms straight.

Mark

 

[steelespike]

Re: My twin boat with Suzuki DF200 with 3x16x20 props has poor hole shot - help?

A boat this size is outside my experience.
We're at about 11000 lbs dry weight yet able to make almost 45 mph.
I'd say pretty impressive running a 32 ft boat almost in a 50 mph bracket.
Pretty obvious by your description, way too much stern weight.
4 blade props as mentioned will help lift the stern should resist ventilation
Will feel smoother and may have better control.
It is usually suggested to drop an inch of pitch when going to a 4 blade.
Hopefully you can find a dealer to let you try props with the understanding your buying a pair.
Its possible your present props could be bow lifting props which would further complicate your problem.
Have you tested the boat with only just enough loaded to test?
I wonder if some water may be lurking somewhere.
Hydro foils may help but I consider them a last resort bandage over a poor setup.
Also if your motors are too low the foils may cause strange handling.

 

[QC]

Re: My twin boat with Suzuki DF200 with 3x16x20 props has poor hole shot - help?

I see tabs full up, and tabs full down, have you tried in between? I doubt this is an issue as adding bow weight helps. That would indicate that the bow is not plowing even with the tabs full down. That indicates, like others have noted, that she is too stern heavy. Anything you can shift forward? I also see the top speed numbers as indicative of something that can ultimately be fixed. However, high speed, big rides usually struggle out of the hole. Tough equation to solve sometimes.

 

[jestor68]

Re: My twin boat with Suzuki DF200 with 3x16x20 props has poor hole shot - help?

I see from the props size that you are likely running Susuki's props. A set of their 15 X 20 4 blade props might work better.

 

[Pioneer320]

Re: My twin boat with Suzuki DF200 with 3x16x20 props has poor hole shot - help?

Thanks for all the advice.

I have now fitted Powertech LS4 4x16x18 props. Have lost about 2 kts off top speed (from 39 to 37), however hole shot is a lot better, no need for trim tabs any more. Can get on the plane with three adults on the back bench and no trim tabs!

The manufacturer (Al Dhaen) had over propped the boat on delivery - clearly aiming at top speed rather than all round performance.

 

[jestor68]

Re: My twin boat with Suzuki DF200 with 3x16x20 props has poor hole shot - help?

Sounds as if you found the solution, provided your WOT rpm is not over the limit.

 

[Texasmark]

Re: My twin boat with Suzuki DF200 with 3x16x20 props has poor hole shot - help?

Even if the rpm is over at WOT and light load you don't have to run it there. I normally run a 24P on my boat which puts me 100+ rpms over max rating at light load, cool temps.

If my sweetie wants to boat with me, which she does now all the time, I have a 21P I use for that, which would also be the right prop for going down to the coast and fishing the shallow tidal shoals......fast hole shot. With that prop exceeding the limit is easy, but I don't have to do it. I punch out and as the rpms get on up there, just ease her back to within range.

HTH,
Mark