motor position

[mausili]

Re: motor position

I don't know if I mentioned this but boat will eventually start to plane it just takes about 30 seconds for the motor to start turning up. Before tabs the bow would rise with tabs not so much. I also have them on stiffest setting.

 

[Texasmark]

Re: motor position

I have gotten 38mph via GPS @ 5300 wot with me and wife in the boat. I have looked at stern when running but that was to see position of tabs which they are right above the water. I can trim the motor a great deal and through peak performance than no change for a bit until it starts to blow out and I will assume that is just before tilt kicks in. I need to see where vent plate is. Bad thing is we have another a weak of cappuccino weather here in St. Augustine.

Not a thing wrong with those numbers, actually perfect. So, your 17P SS is the perfect prop if we can get over the hole shot. When you said 30 seconds to plane out, what is the trim position when you can plane out in that period of time? Is it coming down from trim way out like you mentioned, or is it with the engine in more of a vertical position when you hit the throttle. If the latter, 30 seconds for all that boat with all that dead rise at the transom is not bad at all, actually great!!!!!!! All I would say that you needed to add to that is to move some stuff away from the transom to lighten the load back there and get your exhaust relief ports above water on your engine. Your trim tabs should be pushing against the water when coming out of the hole shot but should be up and out of the water if you don't need them at WOT.

Not sure I need the picture of the engine running at WOT I asked for. The numbers you just gave me are as indicated.

Other than the relief ports in the water, maybe you are just being picky, Grin.

Mark

 

[mausili]

Re: motor position

that is when taking off with trimmed all the way in motor has no responce at all for at least 30 seconds. taking off when motor up boat plains in the time it takes for the trim to go down. it just sucks to know this boat has the potential to take off pretty decent with these tabs. it is also a pain being on this trim motor all the time, even with throttling down to a stop i have to raise motor so water doesnt come over the cowlin.

 

[mausili]

Re: motor position

also only thing in stern is two batteries, which i plan on putting under cc. i have had my wife and 4 kids in the bow and no difference.

 

[Texasmark]

Re: motor position

Ok. We have been through what needs to happen. You have to figure out what you can adapt to your situation to make it happen. Like I said, if I were standing next to you I might could offer you some ideas, but I'm not so this is the best I can do.

Mark

 

[Texasmark]

Re: motor position

One more question. What size holes are already in your prop? Idea here is that you just take your prop to a shop and let them enlarge them bit by bit until you get what you need. May take 2-3 trips but would be your cheapest solution.

Mark

 

[mausili]

Re: motor position

I think for now I am going to focus on raising motor where the 2 colors meet. I will prototype and test with steel than go to alum if it works. I will slot the bottom hole like a conventional motor I will just need to pay attention to the height of plate so I can put about 3 holes in it for adjusent. I think I will start at 2".

 

[Texasmark]

Re: motor position

I think for now I am going to focus on raising motor where the 2 colors meet. I will prototype and test with steel than go to alum if it works. I will slot the bottom hole like a conventional motor I will just need to pay attention to the height of plate so I can put about 3 holes in it for adjusent. I think I will start at 2".

This is your boat and your resolve, but if I had a picture of how far the engine is in the water at max performance speed/trim, and you told me how large your holes were I might save you some grief and maybe some money.....but sir the call is yours...my comments are worth what you paid for them.

Mark

 

[mausili]

Re: motor position

Yeah I will definitely post that info. Like I said we having alot of well needed rain here in north Florida so it could be about a week before I can get it out. As far as prop holes will post them tomorrow afternoon.

 

[mausili]

Re: motor position

Prop holes are 5/16

 

[Texasmark]

Re: motor position

Prop holes are 5/16

I'm surprised you are not getting some performance enhancement from that. My boat is nothing like yours and I put 1/4" holes in mine noticing a difference. I'm running a 90 hp on a light 17' boat. Might ask a prop shop what size holes come in. I'm thinking the Laser II with no plugs are like 1/2". They are huge. One thing for sure. If you get enough exhaust gas across the blades you WILL notice a difference. Like I said, open them up till it works for you. If you get them too big you can seal them back up or plug them.

I ran some quick numbers and your current holes are 1.5 times the area of mine. But you are running a completely different setup and I am not surprised all that much. If you worked your way out to 1/2" you would have 2.5 times the area you currently have and since everything is linear for that (pv=kt where k is a constant of proportionality, p and t should be identical in both tests) you should get proportional additional gas across the blades. Maybe punch out to 3/8" on the first try and let's see what that buys you. However, I still would like to see that picture of how low the engine sits in the water at optimum performance before you mess with the holes. It may be well worth the wait. I noticed the heavy rains in the news the other day over there. Funny, these days we either get a monsoon or a drought.

Mark

 

[mausili]

Re: motor position

Do u want wot trimmed out or cruising speed.

 

[Texasmark]

Re: motor position

Bump.

I put a lot of time into this thread and would really like to know how things work out. Soooo I will attempt to keep it visible.

Bare with me.

Mark

 

[mausili]

Re: motor position

Still waiting for rain to stop. I swear it has rained every day since memorial day. It has been raining this morning with 20mph winds. I guess we'll see what tomorrow brings.

 

[mausili]

Re: motor position

Finally got out today. At wot throttle trimmed out was pretty hard to see anything due to tab spray. But I could see at front of foot the water was half way between AV plate and the next plate up. So not thinking that inch was enough to go through the trouble of raising motor I drilled prop holes to 3/8. Prop responded to throttle. It turned about 5100-5200 till planing than dropped to 4800-4900.

 

[Texasmark]

Re: motor position

Finally got out today. At wot throttle trimmed out was pretty hard to see anything due to tab spray. But I could see at front of foot the water was half way between AV plate and the next plate up. So not thinking that inch was enough to go through the trouble of raising motor I drilled prop holes to 3/8. Prop responded to throttle. It turned about 5100-5200 till planing than dropped to 4800-4900.

Ok. Perfect!!!! got the perfect response; that is exactly what you wanted it to do. Now let's look at your rpm's. Paying attention to your numbers, notice you got throttle response at the higher rpms. That is talking to you. It's saying please cut the pitch. I think OMC runs 4500-5500 rpms. I KNOW, especially with you just said that your rig will run much much better with less pitch. You will probably loose a couple of mph at WOT but your concern is hole shot and I think you wouldn't mind sacrificing a little top end for a reasonable hole shot.

Sooo moving your 4800 up to 5500 is 700 rpm/200 = 3.5". That says that you really could stand to drop your pitch at least 2" and possibly 4" to get your WOT at the upper limit of your recommended rpm range.....that is where you adjust pitch. This would have a stellar impact on your hole shot.l

Soooooo now, do you have a prop shop change the pitch of your current prop or buy another similar shaped SS prop that is ported? You are gaining 300 rpm with your 3/8" holes in the hole, and even if you could max out your rpm's in the hole you would only be upping 300 over the limit which isn't even worth discussing. I know a shop can modify your prop 2", 4 may be stretching it. The neat thing about just bending the blades, is that you haven't added yet another variable like COULD happen with a new prop.

So either check with them or find a similarly shaped SS (blade shape) with 3/8" ports at 15" pitch, let the diameter, 13+" fall where it falls...part of the prop design, and go for it. Less pitch will also help you to control the boat speed easier when cruising. The rpm's will more readily stay where you set them rather than up and down as the boat tries to fall back off plane and you up the rpms then it's too fast and you back off, etc. etc.

The engine is NOT too low on a rig like that. Would be better if you could see the AV plate while running, but with the engine mounted as it is, it could cause you some ventilation problems in rough water.....I'd leave it alone.

Your problem is solved my man. Just execute the grand finale.

Mark

 

[mausili]

Re: motor position

4800 is motor trimmed in still trimmed out is 5300-5400 at 36mph via GPS phone app. The 38 MPH I gave before was with a hand held GPS. As far as ingestion should I seal cowling vents andtube intake from Hull. I know it is or will happen water is right under the shroud below cowling. With the wot I just posted can I still drop in pitch or live with what I have. I know that's alot of boat in the water

 

[mausili]

Re: motor position

Also mark what are your thaughts on drilling the 15" aluminum for ****s and grins

 

[mausili]

Re: motor position

Just reading back through your post. When the rpms dropped that is when the prop holes were are no longer working. Hope that makes sense. As far as the boat coming off plane speed don't really have that answer. 5100 rpm is from stand still taking off. Motor turns 5100 till boat planes than the prop holes are bipassed. Than rpm drops to 48 4900 until I trim it out to 5400.

 

[Texasmark]

Re: motor position

Just reading back through your post. When the rpms dropped that is when the prop holes were are no longer working. Hope that makes sense. As far as the boat coming off plane speed don't really have that answer. 5100 rpm is from stand still taking off. Motor turns 5100 till boat planes than the prop holes are bipassed. Than rpm drops to 48 4900 until I trim it out to 5400.

Yes to the first half, that is how the holes work. On the second half, i.e. you trim out to your 5400 rpm sweet spot, now you make me think that you don't want to tweak your prop at all; change pitch.

Soooooo, is your hole shot acceptable? If so go out and have fun and forget all this. Come back to the answer to this question and I will respond.....am at my computer now so if you are too you will get your answer within the hour.

Mark