Height outboard or modify propeller

[Marco128]

Hello everyone, i'm italian, I have a 6 meter wooden boat with a johnson 175 ocean runner and a 24 raker ho propeller... I have the problem that at maximum speed the propeller does not grip on the water (the booklet engine should do 5200 rpm and now it does 5600 rpm) ratio 1.87, max speed 61 mph(52,53 knots) weight boat 680 kg + 170 kg johnson 175 hp, Tips for increasing the maximum speed? Thanks so much

[rgsauger]

Welcome to scream and fly! Can you post a few more pics of your boat and Hull?

[Marco128]

[Marco128]

Welcome to scream and fly! Can you post a few more pics of your boat and Hull?

[VkingMike]

From the first picture, it looks like the motor may be mounted a bit too high.

[Marco128]

From the first picture, it looks like the motor may be mounted a bit too high.

If I lower the engine, do I not lose top speed? Or is this propeller not suitable for working so high? Thanks for collaboration

[rock]

Welcome to the site. You are actually set up pretty well. 1500 pound boat with only 175 motor at 61 mph not bad. You are correct that lowering motor may slow you down a bit but in my opinion to go any higher, to gain speed, you will need a surfacing prop such as maybe a chopper. Good luck.

Rock

[Marco128]

Thank you so much for the advice, with the new season I will follow your advice and update you, good racing

[MrG]

A SRX 24 will work without modifications or have a 2 degree leading edge cup added to the Raker that worked for me ��
(Any over the hub prop will slip a lot getting on plane and slower speeds with load using more fuel with higher engine rpm )

[Marco128]

Yes I would like to try to lower the motor a little to see the maximum speed, if it decreases the maximum speed I bring it back to this setting and I try to modify the propeller, rpm max 5200, current rpm 5600, perhaps by increasing the degrees I increase a bit the maximum speed

[Jimboat]

Marco - nice looking boat! For your boat weight and power, it seems that you're getting pretty good performance as set up. it looks from your pictures, that your lower unit 'bullet' is about -4 Inches below the vee bottom keel? If so, then i'd think with this setup you'd see about 62mph top speed. If your RPM is indeed 5600rpm to get 61mph, then your 24" Raker is giving you around 13% slip, which is not bad for your boat and setup.

Your boat/setup probably sees 'hump zone' at around 35mph, and with engine height at -4inches, you should be seeing pretty solid acceleration without much slip. Raising engine may increase top speed a little, but you're already topped out at max RPM (5500) for that engine. If you can still get sufficient water pressure for engine cooling with higher engine, you might be able to try different prop. Overall, however, i think you're set up pretty well for your rig.

[David]

Pretty cool boat. Is it your design?

[Marco128]

Thank you very much for the compliments, yes you said well, the prop shaft is 4 inches lower than the V, my raker now does 400 rpm more than the maximum rpm that the engine must do, removing 400 rpm and bringing the raker 24 to 25 say I have a speed gain? Thanks again, in Italy people are not as passionate as you / me are

[Marco128]

I requested the boat so from a craft yard in Venice (Italy), I am attaching a photo of its very spacious interior, they also make the version with the front guide and closed tip

[Marco128]

Yes I would like to try to lower the motor a little to see the maximum speed, if it decreases the maximum speed I bring it back to this setting and I try to modify the propeller, rpm max 5200, current rpm 5600, perhaps by increasing the degrees I increase a bit the maximum speed